This is a Strengthen question.
The difficulty of this question mostly comes from the attractiveness of the wrong answers and a complication to an otherwise simple argument form. Stripping the wrong answers away and simplifying the conclusion reveal a common recurring pattern. The stimulus contains a correlation premise followed by a causal conclusion. The correct answer choice precludes an alternate hypothesis. But like I said, the actual argument is more complex and the presence of four very attractive wrong answers also works to obscure the pattern.
The stimulus starts with a dentist reporting data from five studies. The data reveals that in Europe, the proportion of children with bad teeth is lower than in the United States. It also tells us that in Europe, water is not fluoridated, whereas in the United States, water is fluoridated. As you can see, this is the classic setup where a phenomenon is presented that correlates with another phenomenon. And we’re invited to infer a causal relationship. Naturally, we want to explain why children in Europe have fewer teeth problems. The stimulus conveniently tells us that in Europe, water is not fluoridated, whereas in the United States, water is.
A simpler version of this argument could have gone like this: Therefore, fluoridated water causes teeth problems for children. This would be the classic A (fluoridated water) is correlated with B (teeth issues), therefore A causes B.
The actual argument is a bit more sophisticated and relies implicitly on the contrapositive argument form. The assumption is that if fluoridated water prevented teeth issues, then the data would have shown healthier teeth in countries with fluoridated water. The data showed just the opposite. So therefore, the actual conclusion states that fluoridated water doesn’t prevent teeth issues.
The reason why the reasoning is vulnerable is the same reason why, in general, arguments of this form fail. Bad causal assumptions. “If fluoridated water prevented teeth issues, then the data would have shown healthier teeth in countries with fluoridated water” would be true only if all other causal factors have been controlled for. Clearly, that didn’t happen. The data did not come from anything resembling an ideal experiment. Rather, it came from observational studies. That means whatever differences between Europe and the United States that may be causally relevant to the health of children's teeth are acting on the outcomes.
Think about this in terms of Weaken. If we wanted to expose the vulnerability of the reasoning, we’d simply point out any causal influence that wasn’t controlled for that could have affected dental health. For example, we could have stipulated that in the United States, children eat a lot more candy, which rots teeth. If that's true, then we found an explanation of the difference in dental health between Europe and the United States that doesn’t suggest that fluoridated water is ineffective. Rather, it may well be that fluoridated water actually protects teeth but that preventative causal impact is being overwhelmed by the decaying causal impact of sugars. Kids in the United States have teeth issues in spite of fluoridated water.
If stipulating this to be true weakens the argument, then precluding it strengthens the argument. This is what Correct Answer Choice (E) does. It tells us that the diets of children in the United States are not generally worse for teeth than those of children in Europe. This generally precludes the entire class of food-related explanations of the difference in dental health of which my sugar explanation was just one specific example. By precluding the entire class of explanations, (E) does not prove the hypothesis to be true. But (E) does strengthen the argument by making the hypothesis just a bit more probable.
Interestingly, had the argument been simpler, that is, had the conclusion simply said that fluoridated water causes teeth problems for children, (E) would still work. In fact, it’d be even more obvious that (E) fit the cookie-cutter mold of precluding an alternative explanation.
A note about strategy under timed conditions. I tend to remind you that given the nature of strengthening and weakening questions that deal in a phenomenon hypothesis, it is difficult to anticipate what the correct answer choice will say. That is true in this question as well, which is why, in general, the best strategy is to use POE even though you’d be exposed to the mischief of the wrong answers.
Answer Choice (B) says nearly all dentists in the United States use dental treatments involving the application of fluoride directly to tooth surfaces. (B) can be eliminated simply by recognizing that the causal direction of fluoride pushes in the opposite direction. The conclusion says that fluoride doesn’t benefit dental health yet (B) implies, by appeal to relevant authority, that fluoride does benefit dental health. Clearly, this does not strengthen the argument. But it also doesn't weaken the argument either if you look closer at the details. Even if it's true that fluoride, when directly applied by dentists to tooth surfaces, is effective for treating dental problems, it still may be true that fluoride in water has no effect on protecting teeth.
Answer Choice (D) says that, on average, children in Europe receive more frequent dental checkups than children in the United States. Rather than precluding an explanation of the differences in dental health, (D) seems to be introducing one. If children in Europe differ from children in the United States in that European children receive more frequent preventative care, then that explains why they have better teeth. This is just like when we contemplated diet as the alternative explanation. If children in Europe had a healthier diet for their teeth or had more frequent preventative care for their teeth, the fact that they have healthier teeth may have nothing to do with the presence or absence of fluoride in their water. This would weaken the argument.
Answer Choice (A) says that toothpaste containing fluoride is widely available in both the United States and Europe. (A) is attractive because in form it looks like it's holding some potential causal factor equal and therefore precluding that factor from accounting for the observed difference in dental health. The problem, however, is in order for (A) to be preclusive, it needs some questionable assumptions.
First, notice that we are being baited to assume that wide availability implies equal usage in children. That is a very specific and arbitrary assumption. Wide availability of fluoride toothpaste in and of itself doesn't bear on the issue. What we actually care about is whether children in Europe and the United States use that widely available fluoride toothpaste to a comparable degree. (A) is silent about that phenomenon.
Second, even if we fixed this first problem, (A) still has another subtler problem. Imagine if the answer said that the use of fluoride toothpaste is comparable for children in the United States and Europe. That would seem to preclude the possibility that European children use more fluoride toothpaste than their American counterparts, and it's this extra usage that accounts for their healthier teeth. Yet this reasoning requires fluoride to be good for teeth when in toothpaste, yet useless for teeth when in water. That's an unwarranted assumption. It's not impossible, but it hardly seems reasonable to assume without evidence.
Answer Choice (C) says dental hygiene is typically taught in elementary school in both Europe and the United States. (C) is attractive in the same way that (A) is attractive. In form it looks like it's holding some potential causal factor equal and therefore precluding that factor from accounting for the observed difference in dental health. In this case, the potential causal factor is whether dental hygiene is taught in school. And (C) precludes the phenomenon where dental hygiene is only taught in elementary school in Europe and not the United States. The problem is that we don't care much about precluding this phenomenon. Because even if dental hygiene is typically taught only in elementary schools in Europe and not the United States, a lot of other causal assumptions need to be supplied in order for the observed difference in dental health to be explained. First, we need to assume that children enact dental hygiene behaviors that they learn in school because otherwise the mere instruction would have no causal impact on their dental health. Second, we also need to assume that just because American children don't learn dental hygiene at school, they don't learn it at all. That seems highly unlikely, since if they're not learning it in school, then parents would have extra incentive to teach dental hygiene at home.
Notice how Correct Answer Choice (E) doesn't suffer from the need to fill in these causal gaps with questionable assumptions. If the diets of children in the United States were generally worse for dental health, then that explains the observed difference in dental health.
This is a Strengthen question.
We’re asked to find support for the paleontologist's hypothesis, which is the conclusion of the argument.
Here we have an argument that presents phenomena followed by a hypothesis that tries to explain the phenomena. We start with the set of dinosaurs, then we move into the subset called ornithomimids, which are birdlike, then we move into a further subset called the later-ornithomimids, which had toothless beaks and weak jaw muscles. A fossil of one particular member of that subset called G. bullatus shows a comblike plate inside its beak. We know that in modern birds like ducks and geese, plates like that are used to strain small bits of food from water and mud. So the argument concludes with a hypothesis that G. bullatus also fed by filtering food from water and mud.
The phenomenon is that G. bullatus has a comblike plate, and the hypothesis explains the function of the beak: for feeding. Support also comes from a premise about modern ducks and geese. That means this argument also uses reasoning by analogy. Therefore, one assumption is that the functionality of the beaks on ducks and geese is relevant as evidence of their function on G. bullatus .
As with most Strengthen and Weaken questions where the stimulus takes the form of phenomena-hypothesis, it's hard to anticipate the right answer choice because there are so many different directions that the question can go. Usually, the best strategy is POE.
Answer Choice (A) says some dinosaurs with toothless beaks and weak jaw muscles are believed to have pursued small prey and to have eaten eggs. First, it’s not clear how this is relevant to G. bullatus. If we assume that the dinosaurs in this answer exhibit similar behavior to G. bullatus, then that's not good for the hypothesis. This reveals that dinosaurs with toothless beaks can feed in some other manner. But this is not an effective Weaken answer choice either precisely because we have no reason to assume that the dinosaurs in this answer exhibit similar behavior to G. bullatus.
Answer Choice (B) says toothless beaks and weak jaw muscles were not common to any dinosaur group other than ornithomimids. All this tells us is that toothless beaks and weak jaw muscles are good evidence that the creature belonged to ornithomimids. If we were trying to identify a particular fossil and it showed signs of toothless beaks and weak jaw muscles, then this information might be helpful. However, the phenomenon we’re trying to explain above is what functionality comblike plates had. (B) doesn't help resolve that issue.
Answer Choice (C) says that except for the comblike plates in their beaks, G. bullatus shared few anatomical features with modern ducks and geese. (C) stresses points of dissimilarity between G. bullatus and modern ducks and geese. Whatever it's doing, it's certainly not strengthening the analogous reasoning above. But it's also not weakening that reasoning either, at least not by much, because (C) doesn't tell us what the few anatomical features that are shared between the two are. It merely tells us that there are few that are shared while most are not shared. But what we really need to know in order to either weaken or strengthen the reasoning by analogy is not just the proportion of similar to dissimilar features, but rather exactly which features are similar or dissimilar, because only the relevant similarities and dissimilarities matter, not all of them.
Correct Answer Choice (D) says most G. bullatus fossils have been found in sediments deposited in lakes, rivers, and other wet environments. This is evidence that corroborates the hypothesis by empirically confirming a prediction. If it's true that G. bullatus fed by filtering food from water and mud, then one would predict that these animals lived near water and mud. And if that's true, then one would expect to find their fossils near wet environments.
This is not dispositive evidence that the hypothesis is true. It is just another piece of evidence that gives a bit more weight to the hypothesis. In other words, it strengthens. You can see this by changing the quantifier on this answer choice. If instead of “most,” it said “nearly half,” or “some,” then the weight of this evidence diminishes accordingly. In fact, if it said “none,” then this would disconfirm a prediction of the hypothesis, which would weaken the hypothesis. Now, you might have concerns in the back of your mind like, “Wait, we’re talking about fossils, and surely after tens of millions of years, the fossils moved around.” Those are legitimate concerns. But I think the answer choice largely takes care of that by telling us that the fossils were found in sediments deposited near wet environments.
Answer Choice (E) says paleontologists have not found evidence that any dinosaur other than G. bullatus had comblike plates. This is similar to (B). If the issue above was that of identification, like if we had to figure out what species a particular fossil belonged to, then (E) may be relevant. If G. bullatus is unique in having comblike plates, then finding a fossil with comblike plates is evidence that the fossil is one of G. bullatus. But this is not the issue in the argument above. Rather, the issue is about the functionality of the comblike plates.
This is a Strengthen question.
We’re asked to find support for the paleontologist's hypothesis, which is the conclusion of the argument.
Here we have an argument that presents phenomena followed by a hypothesis that tries to explain the phenomena. We start with the set of dinosaurs, then we move into the subset called ornithomimids, which are birdlike, then we move into a further subset called the later-ornithomimids, which had toothless beaks and weak jaw muscles. A fossil of one particular member of that subset called G. bullatus shows a comblike plate inside its beak. We know that in modern birds like ducks and geese, plates like that are used to strain small bits of food from water and mud. So the argument concludes with a hypothesis that G. bullatus also fed by filtering food from water and mud.
The phenomenon is that G. bullatus has a comblike plate, and the hypothesis explains the function of the beak: for feeding. Support also comes from a premise about modern ducks and geese. That means this argument also uses reasoning by analogy. Therefore, one assumption is that the functionality of the beaks on ducks and geese is relevant as evidence of their function on G. bullatus .
As with most Strengthen and Weaken questions where the stimulus takes the form of phenomena-hypothesis, it's hard to anticipate the right answer choice because there are so many different directions that the question can go. Usually, the best strategy is POE.
Answer Choice (A) says some dinosaurs with toothless beaks and weak jaw muscles are believed to have pursued small prey and to have eaten eggs. First, it’s not clear how this is relevant to G. bullatus. If we assume that the dinosaurs in this answer exhibit similar behavior to G. bullatus, then that's not good for the hypothesis. This reveals that dinosaurs with toothless beaks can feed in some other manner. But this is not an effective Weaken answer choice either precisely because we have no reason to assume that the dinosaurs in this answer exhibit similar behavior to G. bullatus.
Answer Choice (B) says toothless beaks and weak jaw muscles were not common to any dinosaur group other than ornithomimids. All this tells us is that toothless beaks and weak jaw muscles are good evidence that the creature belonged to ornithomimids. If we were trying to identify a particular fossil and it showed signs of toothless beaks and weak jaw muscles, then this information might be helpful. However, the phenomenon we’re trying to explain above is what functionality comblike plates had. (B) doesn't help resolve that issue.
Answer Choice (C) says that except for the comblike plates in their beaks, G. bullatus shared few anatomical features with modern ducks and geese. (C) stresses points of dissimilarity between G. bullatus and modern ducks and geese. Whatever it's doing, it's certainly not strengthening the analogous reasoning above. But it's also not weakening that reasoning either, at least not by much, because (C) doesn't tell us what the few anatomical features that are shared between the two are. It merely tells us that there are few that are shared while most are not shared. But what we really need to know in order to either weaken or strengthen the reasoning by analogy is not just the proportion of similar to dissimilar features, but rather exactly which features are similar or dissimilar, because only the relevant similarities and dissimilarities matter, not all of them.
Correct Answer Choice (D) says most G. bullatus fossils have been found in sediments deposited in lakes, rivers, and other wet environments. This is evidence that corroborates the hypothesis by empirically confirming a prediction. If it's true that G. bullatus fed by filtering food from water and mud, then one would predict that these animals lived near water and mud. And if that's true, then one would expect to find their fossils near wet environments.
This is not dispositive evidence that the hypothesis is true. It is just another piece of evidence that gives a bit more weight to the hypothesis. In other words, it strengthens. You can see this by changing the quantifier on this answer choice. If instead of “most,” it said “nearly half,” or “some,” then the weight of this evidence diminishes accordingly. In fact, if it said “none,” then this would disconfirm a prediction of the hypothesis, which would weaken the hypothesis. Now, you might have concerns in the back of your mind like, “Wait, we’re talking about fossils, and surely after tens of millions of years, the fossils moved around.” Those are legitimate concerns. But I think the answer choice largely takes care of that by telling us that the fossils were found in sediments deposited near wet environments.
Answer Choice (E) says paleontologists have not found evidence that any dinosaur other than G. bullatus had comblike plates. This is similar to (B). If the issue above was that of identification, like if we had to figure out what species a particular fossil belonged to, then (E) may be relevant. If G. bullatus is unique in having comblike plates, then finding a fossil with comblike plates is evidence that the fossil is one of G. bullatus. But this is not the issue in the argument above. Rather, the issue is about the functionality of the comblike plates.
This is an RRE question.
The stimulus begins by telling us that when a healthy gazelle is frightened by hunters in a truck, they run away quickly and efficiently and hide themselves. So that is not surprising. The next sentence is where the surprising phenomenon starts. Notice the word “but” that introduces the phenomenon. It says that when a healthy gazelle detects an approaching lion, it does this thing called “stotting.” Stotting is where it leaps really high into the air as it's running away. Stotting has two consequences: one is that it uses a lot of energy that could have been used in running away, and the other is that it actually draws the lion’s attention. So therein lies the puzzle. Why do gazelles stot?
As is generally the case with RRE questions, how surprising the phenomenon is lies on a spectrum which turns on the kinds of assumptions we bring into the facts. In general, we tend not to know very much about the subject matter being discussed. Because of that, we tend to bring in pretty naïve assumptions. So in this instance, the naïve assumption that we might bring in would be that gazelles wouldn’t exhibit behavior such as stotting, which draws attention of the predator and which uses energy that could have been better spent on running away. But if you ask a subject matter expert, like a biologist who studies gazelles, she probably won't have the same set of assumptions that we do. She might already know what the explanation is for stotting.
Anyway, we don't have to be subject matter experts. We just have to understand the scientific logic that underpins this question. That’s the logic of phenomenon and hypothesis, the logic of causation.
Correct Answer Choice (C) says that to animals that typically prey on gazelles, which is to say, lions and cheetahs, stotting is a signal of strength and ability to escape. Okay, so this being an answer choice, we have to take it to be true. The question is whether the truth of this phenomenon explains the above phenomenon. The answer is yes. If stotting signals to a lion that this gazelle is strong and has the ability to escape, then the lion, presumably, is less likely to pursue that particular gazelle. I say presumably because it’s not explicitly stated. But that's a fairly reasonable assumption.
Answer Choice (A) says that animals that are startled sometimes act in ways that appear irrational to human observers. This answer choice at best restates the phenomenon instead of explaining the phenomenon. First we should acknowledge that there is nothing irrational about gazelles running away when they are frightened by hunters, so this answer isn't talking about that phenomenon. So the only phenomenon left is the phenomenon of stotting. And, indeed, the only reason why the question stem says there's an apparent paradox is because stotting appears to be irrational. It seems irrational that a gazelle would waste energy and draw the predator’s attention. That’s what we’re trying to explain. But you can’t “explain” it just by saying it seems irrational. You haven’t explained anything.
Answer Choice (B) says that young gazelles and gazelles that are not very healthy often stot when they become frightened by humans or by loud machines. This is a common type of wrong answer in RRE. This answer choice presents a phenomenon that is consistent with the phenomenon above and is similarly in need of an explanation. Having read this answer, I still don't understand why healthy gazelles stot when they detect a lion. In addition to that, I now have to wonder why young and unhealthy gazelles also stot when they are frightened by humans or loud machines.
Answer Choice (D) says a healthy gazelle can usually detect the approach of a predator before the predator becomes aware of the presence of the gazelle. In this competition between predator and prey, it's an enormous advantage to be more sensitive to the other’s presence. This answer reveals that it's the prey that's more sensitive. Okay, so that means the gazelle enjoys the first mover advantage. It can start running away before the lion even realizes that it's there. But this still doesn't explain why the gazelle stots as it runs away, especially when we were already told that stotting draws the lion's attention to the gazelle. Why not just run away without stotting?
Answer Choice (E) says that lions cannot run as quickly as gazelles, but they can still be effective by hunting in groups and coordinating. This answer choice reveals more information about how lions hunt. But it doesn't explain why gazelles stot. This answer is inviting us to make an unwarranted assumption that somehow stotting thwarts the lions' coordinated group hunting efforts. I have no reason to believe that's true. It seems, in fact, more likely that not stotting, which is to say, just straight up running away as fast as you can without showing off, would be the more effective strategy to escape a coordinated group attack.
A
Animals that are startled sometimes act in ways that appear irrational to human observers.
B
Young gazelles and gazelles that are not very healthy often stot when they become frightened by humans or by loud machines.
C
To animals that typically prey on gazelles, stotting is a signal of strength and ability to escape.
D
A healthy gazelle can usually detect the approach of a predator before the predator becomes aware of the presence of the gazelle.
E
While not able to run as quickly as gazelles, predators such as lions hunt effectively by hunting in groups and coordinating their attacks.
This is a Weaken question.
The stimulus is an advertisement that states Omnicide kills more species of insects than any other insecticide. From that premise, the advertisement concludes that Omnicide is the best insecticide for home gardeners, especially the ones who can't tell which insects are harming their plants.
But just because an insecticide kills the widest variety of insects doesn't mean that that's the best insecticide. A gardener who wants to protect her plants only wants to kill the harmful insects. This means the assumption in the advertisement's argument is that Omnicide kills only the harmful insects. Now, if that assumption is true, then the argument is pretty great. Omnicide is killing the widest variety of harmful insects. A gardener who doesn't know which insect is harming her plant should get Omnicide because it casts a wide net and increases the chances of killing the mystery pest.
But if that assumption were false, then this argument is severely weakened. Correct Answer Choice (B) cuts against that assumption. It says many insect species are beneficial to garden plants and Omnicide kills most of them. This weakens the argument to the point of directly damaging the conclusion. (B) is so powerful that it actually supports the opposite of the conclusion. This isn’t something that a correct answer in a Weaken question needs to do, but it is something that frequently occurs. Just be mindful that while some answers overshoot the standard, it doesn’t mean that they’re setting the standard.
Answer Choice (A) says some of Omnicide's competitors kill almost as many species of insects as Omnicide does. This doesn't weaken the argument. If anything, this only explicitly confirms that the competitors do not kill as many insects as Omnicide does.
Answer Choice (C) says merely protecting plants from attack by insect pests does not guarantee that the plants will be healthy. This is irrelevant. It could have been relevant if the conclusion were about the general health of plants. If that were the case, then of course damage from insects is only a partial consideration. We would also want to control for things like sunlight, nutrition, soil conditions, etc. But the conclusion is just about protecting plants from harmful insects.
Answer Choice (D) says Omnicide is more profitable for the manufacturer than most of their other insecticides. This is a classic bait trying to attack an argument by attacking the source. It doesn't work. The strength of the reasoning doesn’t turn on the profits. It might explain why the company is advertising Omnicide as opposed to another of their products, but that’s not our job here.
Answer Choice (E) says Omnicide does not kill weeds or mammalian pests like gophers or groundhogs. Similar to (C), this is not relevant because the conclusion is just about protecting plants from harmful insects. Again, this could have been relevant if the conclusion were about protecting plants from harm in general. If that had been the case, then other weeds or mammalian pests would be relevant considerations.
This is a Weaken question.
The stimulus is an advertisement that states Omnicide kills more species of insects than any other insecticide. From that premise, the advertisement concludes that Omnicide is the best insecticide for home gardeners, especially the ones who can't tell which insects are harming their plants.
But just because an insecticide kills the widest variety of insects doesn't mean that that's the best insecticide. A gardener who wants to protect her plants only wants to kill the harmful insects. This means the assumption in the advertisement's argument is that Omnicide kills only the harmful insects. Now, if that assumption is true, then the argument is pretty great. Omnicide is killing the widest variety of harmful insects. A gardener who doesn't know which insect is harming her plant should get Omnicide because it casts a wide net and increases the chances of killing the mystery pest.
But if that assumption were false, then this argument is severely weakened. Correct Answer Choice (B) cuts against that assumption. It says many insect species are beneficial to garden plants and Omnicide kills most of them. This weakens the argument to the point of directly damaging the conclusion. (B) is so powerful that it actually supports the opposite of the conclusion. This isn’t something that a correct answer in a Weaken question needs to do, but it is something that frequently occurs. Just be mindful that while some answers overshoot the standard, it doesn’t mean that they’re setting the standard.
Answer Choice (A) says some of Omnicide's competitors kill almost as many species of insects as Omnicide does. This doesn't weaken the argument. If anything, this only explicitly confirms that the competitors do not kill as many insects as Omnicide does.
Answer Choice (C) says merely protecting plants from attack by insect pests does not guarantee that the plants will be healthy. This is irrelevant. It could have been relevant if the conclusion were about the general health of plants. If that were the case, then of course damage from insects is only a partial consideration. We would also want to control for things like sunlight, nutrition, soil conditions, etc. But the conclusion is just about protecting plants from harmful insects.
Answer Choice (D) says Omnicide is more profitable for the manufacturer than most of their other insecticides. This is a classic bait trying to attack an argument by attacking the source. It doesn't work. The strength of the reasoning doesn’t turn on the profits. It might explain why the company is advertising Omnicide as opposed to another of their products, but that’s not our job here.
Answer Choice (E) says Omnicide does not kill weeds or mammalian pests like gophers or groundhogs. Similar to (C), this is not relevant because the conclusion is just about protecting plants from harmful insects. Again, this could have been relevant if the conclusion were about protecting plants from harm in general. If that had been the case, then other weeds or mammalian pests would be relevant considerations.
This is a Weaken question.
The argument starts with a report of what some people believe. They believe that the economic benefits of genetically engineered foods may be offset by the hidden health risks. That's the context, that's other people's position. The author, who is a scientist, signals the transition to argument with the word “however.” She hits us with her conclusion that the risk, referring to the risk to human health, is minimal. Why should we believe this conclusion? The rest of the stimulus provides reasons.
The first premise is that in most cases of deliberate alteration of a plant's genetic structure, only a single gene out of 750,000 is changed. She then says that since the change is so slight, it cannot have effects significant enough to be worrisome.
There are many assumptions in this argument but perhaps the most crucial assumption is whether a single gene change can cause effects significant enough to be worrisome. If it's true that the alteration of a single gene cannot have effects significant enough to be worrisome, then her conclusion follows pretty strongly. It does seem like the risk, from plant foods anyway, is minimal. However, if it's not true, if even a single genetic alteration is capable of producing significant effects to be worrisome, then her argument is severely weakened.
This is what Correct Answer Choice (D) reveals. It says that there are plants that are known to be toxic to some animals and whose toxicity is known to be affected by the alteration of a single gene. (D) reveals that indeed it is possible for the alteration of a single gene to have effects significant enough to be worrisome. This suggests that the crucial assumption in the argument is false. Note that this answer does not overshoot the requirement of Weaken questions. If you object to this answer on the grounds that we don't know if these plants in (D) are analogously similar to the plants that we're talking about in the stimulus, then you are trying to do too much. You're trying to prove the opposite of the conclusion. In other words, you're trying to prove that there is a significant risk to human health from the alteration of a single gene in, say, the corn that we grow. Indeed, to do that, we do need to show that the alteration of a single gene in corn results in toxicity. But that's not what we're trying to do. We're just trying to weaken the argument. (D) easily crosses that threshold.
Granted we didn't talk about the other assumptions that the argument made. Another big one is that the premises only talk about altering a plant's genetic code. The conclusion is more broadly stating that the risk of foodstuffs in general is minimal. That includes meat and other animal products as well.
Answer Choice (A) says the genetically engineered plants that have been developed so far have few advantages over plants that are not genetically engineered. If the argument above worked on a cost-benefit logic, then (A) might be relevant. Even so, (A) only explicitly confirms that there are advantages, just not that many of them. But the affirmation of the advantages that do exist, few as they are, has no bearing on any of the assumptions made in the actual argument.
Answer Choice (B) says whatever health risks there are in foods from genetically altered plants may be somewhat reduced by other factors. And then it goes on to state what those factors are. This being true does not weaken the argument. Notice that (B) doesn't take a position on whether health risks exist. It just says that if those health risks exist, they may be reduced. So in the world in which health risks exist, (B) provides ways to mitigate that risk. But that's not what we're talking about. We're trying to figure out if we are in a world where the risk is significant or if we are in a world where the risk is minimal.
Answer Choice (C) says scientists have yet to determine for each characteristic of some plants and animals used for food the precise location of the genes that determine a characteristic. If we are able to parse this statement, I think we'll see that it has no bearing on the argument. What the statement is saying is that we don't have a complete mapping of the observable characteristics (phenotype) of plants and animals onto the genes that are responsible for those characteristics. So, for example, we might observe that a particular variety of corn happens to be highly resistant to heat, or that it may be very fragrant, or that it grows really well regardless of the time of year. Those are all observable characteristics (phenotypes) that are controlled by genes. (C) is saying that we just don't know which genes control those characteristics. That's totally fine. The argument doesn't require a complete mapping of genes to observable characteristics. It just requires the assumption that a small change in a single gene can't have significant negative effects that we should worry about.
Answer Choice (E) says the research has shown that those consumers who are most strongly opposed to genetically altered foods tend to be the most ill-informed on the issue. Again this has no bearing on the argument. The argument is about whether a single genetic alteration can produce effects that warrant concern. How consumers feel about this is utterly irrelevant. (E) tells us that the consumers who are most strongly opposed are most ill-informed and the consumers that are least opposed are best-informed. That makes sense but it has nothing to do with the argument.
A
The genetically engineered plants that have been developed so far have few advantages over plants that are not genetically engineered.
B
Whatever health risks there are in food from genetically altered plants may be somewhat reduced by other factors such as enrichment of the plants’ vitamin and mineral content.
C
Scientists have yet to determine, for each characteristic of some plants and animals used for food, the precise location of the genes that determine that characteristic.
D
There are plants that are known to be toxic to some animals and whose toxicity is known to be affected by the alteration of a single gene.
E
Research has shown that those consumers who are most strongly opposed to genetically altered foods tend to be ill-informed on the issue.
This is a Strengthen question.
The argument begins with a phenomenon that a certain ancient society burned large areas of land. Naturally, we wonder why they did this. The author presents other people's hypothesis: they burned large areas of land to prepare the ground for planting, which means that the ancient society was beginning the transition to agriculture.
To test this hypothesis, we can check its predictions. One prediction would be evidence of agriculture. If it's true that they burned the ground in preparation for planting, then we should expect to find evidence of agriculture. But we have little evidence of cultivation after the fires. This strongly implies that the other people's hypothesis of transition to agriculture is wrong. And so the author concludes it is likely that the society was still a hunter-gatherer society.
Now, one quick assumption you might've noticed is whether ancient societies fall into the binary buckets of either agricultural or hunter-gatherer. That is something to keep in mind, but as it turns out, those two buckets do largely capture all societies. The answer choices don't try to undercut that assumption.
But don't forget that we still have this phenomenon presented in the beginning argument. The author hasn't given an explanation of why the ancient society burned large areas of land. She has only, rather effectively, disposed of a bad explanation.
This is where Correct Answer Choice (D) improves the reasoning of the argument. It says hunter-gatherer societies are known to have used fire to move animal populations from one area to another. This presents a plausible explanation of the phenomenon unexplained in the original argument. If this is true, then that phenomenon itself becomes support for the author's conclusion that the society was still a hunter-gatherer society.
Answer Choice (A) says many ancient cultures had agriculture before they began using fire to clear large tracts of land. This means that fire clearing of land is not necessary for the transition to agriculture. That's good to know if you were curious about early human civilization. But this has nothing to do with the argument. The fact is the particular ancient society we’re talking about did clear large areas of land with fire. We’re trying to figure out what that means about the status of their civilizational development.
Answer Choice (B) says hunter-gatherer societies use fire for cooking and for heat during cold weather. This doesn't affect the argument at all. The argument told us that this particular society used fire to burn large areas of land and then we try to argue that this particular society was still a hunter-gatherer society. Information about hunter-gatherer societies using fire to do other things doesn't help the claim.
Answer Choice (C) says many plants and trees have inedible seeds that are contained in hard shells and are released only when subjected to the heat of a great fire. This is probably the most attractive wrong answer choice because it also looks like it's trying to provide an explanation for the phenomenon described above. It's trying to suggest that the reason why the ancient society burned large areas of land was to extract the seeds from the hard shells. There are at least two problems with (C), however. The first problem is that the seeds are inedible. That means you can't eat them. So what are you trying to do by extracting them? One plausible explanation is that you're trying to plant them. But that's not good for this argument, because that suggests that the culture might have been agrarian. The other problem is that this explanation doesn't fit very well with the phenomenon. Even if it's true that the seeds are released only when subjected to the heat of a great fire, it's not clear that the way to extract a seed is to burn down an entire tract of land. Why not collect all the shells and just burn them? Wouldn’t that be easier than setting a whole forest on fire? Notice (D) doesn't suffer from this problem. The hypothesis fits the facts. If you're trying to move entire populations of animals, then burning large areas of land makes sense. The solution is at the right scale for the problem.
Answer Choice (E) says few early societies were aware that burning organic material can help create nutrients for soil. This suggests the preclusion of a potential explanation. Before reading (E), one potential explanation for why the ancient society burned large areas of land was to fertilize the soil. After reading (E), it seems less likely that that's what our ancient society was attempting to do. What is the significance of this? I suppose it's less likely now that our ancient society was agrarian. But this was already established in the argument.