"Surprising" Phenomenon
Even though some bird and reptile species’ use of hissing as a threat device is likely to have developed in an early common ancestor, that common ancestor’s predators would not have been able to hear such hissing sounds.
Objective
The right answer will provide an alternate explanation for the common ancestor’s hissing. It will be a hypothesis that explains how the common ancestor’s hissing might have been useful as a threat device against potential predators, even though those predators could not hear the hissing.
A
Like its potential predators, the common ancestor of bird and reptile species would have lacked the anatomy necessary to hear hissing sounds.
The common ancestor’s inability to hear its own hissing does not provide any explanation for why it would have developed hissing in the first place. We need an answer that explains why hissing was advantageous for the common ancestor, even though its predators couldn’t hear it.
B
The common ancestor of bird and reptile species would probably have employed multiple threat devices against potential predators.
Even if the common ancestor defended itself in other ways, we still need an explanation for why the common ancestor developed hissing as a threat device even though its predators could not hear it. There must be some other reason for using hissing as a threat device.
C
The production of a hissing sound would have increased the apparent body size of the common ancestor of bird and reptile species.
This gives a reason why the common ancestor’s hissing might have been useful against predators: it made the animal seem larger. This explains why it developed hissing sounds, even though its predators couldn’t hear them.
D
The use of hissing as a threat device would have been less energetically costly than other threat behaviors available to the common ancestor of bird and reptile species.
Whether hissing was energetically costly does not explain why the common ancestor used it as a threat device even though predators couldn’t hear it. We need an answer that gives a different reason for using hissing as a threat device.
E
Unlike most modern bird and reptile species, the common ancestor of these species would have had few predators.
Even if the common ancestor had few predators, it would still have needed to defend itself against those predators. So, we still need an alternate reason that explains why the common ancestor developed hissing as a threat device.
Summarize Argument
The editor concludes that the city’s claim about its new recycling program are absurd. This is because the same overall volume of recyclables will be collected, just over a greater number of collections.
Notable Assumptions
For the city’s claim to be absurd, the editor must assume that there could be no other benefits to the new collection schedule besides increasing the overall volume of recyclables collected. Since that volume will stay the same, the editor can’t see how the collection cycle could possibly be beneficial.
A
The cost of collecting and disposing of general trash has been less than the cost of collecting and disposing of recyclables, and this is still likely to be the case under the new recycling program.
We don’t care about general trash. We need to know whether the new recycling program will live up to the city’s claim.
B
Even if the volume of collected recyclables increases, that increase might not be enough to make the recycling program cost effective.
The city never claims the program will hit some arbitrary threshold of “cost effective.” It simply claims the program will be more cost effective.
C
Because the volume of recyclables people accumulate during a week is less than what they accumulate during two weeks, the city expects a recyclables pickup to take less time under the new program.
While a pickup will take less time, we have no idea how long two pickups every two weeks will take versus one pickup every two weeks. The author’s argument remains intact if those two pickups together take as long, or longer, than the single biweekly pickup.
D
A weekly schedule for recyclables pickup is substantially easier for people to follow and adhere to than is a schedule of pickups every other week.
While the overall volume will stay the same, people are more likely to put out their recyclables on a weekly schedule. Thus, the city will collect and sell more recyclables than before.
E
Because of the increase in the number of pickups under the new program, the amount charged by the contractor that collects the city’s recyclables will increase significantly.
This strengthens the author’s argument. The new recycling program won’t just be the same as before—it’ll be even more expensive.
Summarize Argument: Phenomenon-Hypothesis
The author concludes that the reasoning power and spatial intuition exercised in chess-playing likely can cause improvement in other intellectual activities. This is based on a study of a group of children who completed a program involving learning how to play chess. Most of the children who completed the program showed a large increase in schoolwork achievement.
Notable Assumptions
The author assumes that the students’ chess-playing causally contributed to their improved schoolwork achievement. The author also assumes a particular causal mechanism — that it was the reasoning power and spatial intuition exercised by chess that improved the children’s schoolwork achievement.
A
Some students who did not participate in the chess program had learned to play chess at home.
And did these students experience an improvement in schoolwork achievement? If we don’t know this, (A) has no impact.
B
Those children who began the program but who did not successfully complete it had lower preprogram levels of achievement than did those who eventually did successfully complete the program.
Pre-program levels of achievement are irrelevant, since the author never compared the absolute achievement levels of the students who completed the program to those of the students who didn’t. We still know the program-completers increased their achievement after the program.
C
Many of the children who completed the program subsequently sought membership on a school chess team that required a high grade average for membership.
This suggests a potential alternate hypothesis for the increase in achievement levels observed in the study. If many of the children wanted to join a team that required a high grade average, that could have motivated these students to do better on their schoolwork.
D
Some students who did not participate in the chess program participated instead in after-school study sessions that helped them reach much higher levels of achievement in the year after they attended the sessions.
The author never assumed that chess is the only activity that can improve student achievement. And, since we have no reason to think that the students who completed the chess program attended the sessions described in (D), this answer has no impact.
E
At least some of the students who did not successfully complete the program were nevertheless more talented chess players than some of the students who did complete the program.
We don’t know whether the students described in (E) experienced an increase in achievement levels. In addition, varyling levels of chess talent don’t necessarily impact the level of reasoning power or spatial intuition exercised during chess.
Researchers working in Western Australia have discovered the oldest fragments of the Earth’s early crust that have yet been identified: microdiamonds. These microscopic crystals measure only 50 microns across and were formed 4.2 billion years ago. This discovery sheds light on how long it took for the Earth’s crust to form, since this date is only 300 million years after the formation of the Earth itself.
Summary
Western Australian researchers have discovered microdiamonds, the oldest fragments of the Earth’s early crust yet identified. These microscopic crystals were formed 4.2 billion years ago, only 300 million years after the formation of the Earth itself. This discovery sheds light on how long it took for Earth’s crust to form.
Notable Valid Inferences
Earth’s crust did not take longer than 300 million years to begin to form.
A
The Earth’s crust took no longer than 300 million years to start to form.
Must be true. We know this because the microdiamonds researchers found were part of the Earth’s early crust. If the microdiamonds existed 300 million years after Earth itself was formed, then Earth’s crust must have taken no longer than 300 million years to begin to form.
B
The Earth’s crust first formed in the area that is now Western Australia.
Could be false. To claim this is where the Earth’s crust first formed is too extreme. We only know that the microdiamonds the researchers found are the oldest fragments to be found to date. It is possible there exists older fragments that have not yet been found.
C
The Earth’s crust took billions of years to form.
Must be false. We know the microdiamonds the researchers found were part of Earth’s early crust, and these existed only 300 million years after the formation of Earth.
D
Microdiamonds were the first components of the Earth’s crust to form.
Could be false. To claim microdiamonds were the first components is too extreme. We only know that they are the oldest fragments identified to date. It is possible that older fragments exist that have not yet been identified.
E
All naturally occurring microdiamonds were formed at the time the Earth’s crust was being formed.
Could be false. To claim all microdiamonds were formed at this time is too extreme. It is possible that there are other naturally occurring microdiamonds that formed after the ones the researchers identified.
Summary
The hairless dogs in Mexico and Peru must have been transported by boat from one of those two countries to the other, and probably during trade.
Why must they have started in either Mexico or Peru? Well, they wouldn’t have just turned up out of nowhere in both countries. Hairlessness likely didn’t originate twice, so both sets of dogs probably originated a single place.
Why must they have come by boat? They’ve never existed in the wild, so to arrive anywhere else, they must have come with humans. And overland travel between Mexico and Peru was very difficult back when these dogs appeared in those countries.
Why must they have started in either Mexico or Peru? Well, they wouldn’t have just turned up out of nowhere in both countries. Hairlessness likely didn’t originate twice, so both sets of dogs probably originated a single place.
Why must they have come by boat? They’ve never existed in the wild, so to arrive anywhere else, they must have come with humans. And overland travel between Mexico and Peru was very difficult back when these dogs appeared in those countries.
Notable Assumptions
The author hypothesizes that boats are the answer because overland travel would have been so difficult. But he never says whether boats were any easier. He’s implying a comparison (overland harder, boats easier) without actually supporting that comparison. So he must assume that travel between the two countries was indeed easier by boat than by land.
He also assumes that the dogs weren’t transported to both Mexico and Peru from some other location(s).
He also assumes that the dogs weren’t transported to both Mexico and Peru from some other location(s).
A
Hairless dogs have never been found anywhere except in the regions of western Mexico and coastal Peru.
The author assumes the dogs weren’t transported to both Mexico and Peru from some other location(s). But he doesn’t assume they’ve never been found anywhere else. What if they were transported from Mexico to Peru, and then to Argentina? That wouldn’t damage the argument.
B
Most of the trade goods that came into western Mexico centuries ago were transported by boat.
Too strong. The author doesn’t need to assume that most trade from all places to Mexico was by boat. He just needs to assume that there were at least some trade expeditions running between Mexico and Peru.
C
Centuries ago, no one would have traveled between western Mexico and coastal Peru by boat except for the purposes of carrying out a trading expedition.
Too strong. The author doesn’t need to assume that all boat travel was for trading expeditions—just that at least some boat travel was (enough to make it likely that the dogs were on some of those expeditions).
D
If hairless dogs were at one time transported between western Mexico and coastal Peru by boat, they were traded in exchange for other goods.
Whether the dogs were traded during trade expeditions is irrelevant. The author merely assumes that there was some way for the dogs to be present on those expeditions. Perhaps they were brought as gifts rather than exchanged, or perhaps they were there by accident.
E
Centuries ago, it was easier to travel by boat between western Mexico and coastal Peru than to travel by an overland route.
The author implies a comparison between overland and boat travel but never says how difficult boat travel was. He must assume boat travel was easier. Otherwise, if it was just as hard or harder than overland travel, the conclusion becomes unsupported or even anti-supported.
Summary
Ostrich farming requires less land than cattle farming. Ostriches reproduce faster than cattle. Starting in cattle ranching requires a large herd of cows, a bull, and at least two acres per cow. Starting in ostrich farming requires two pairs of yearling ostriches and one acre of land. The start-up costs for ostrich farming is greater than that for cattle farming. Ostrich farming can eventually yield five times the returns as cattle farming.
Strongly Supported Conclusions
Ostrich farming allows farmers to eventually produce greater yields with less land than cattle ranching. Two pairs of yearling ostriches plus one acre of land is more expensive than a large herd of cows, a bull, and two acres per cow.
A
Two pairs of yearling ostriches are more expensive than a herd of cows and a bull.
This is strongly supported since we know that the start-up costs for ostrich farming is higher than that for bull farming, and starting an ostrich farm requires two pairs of yearling ostriches compared to a herd of cows and a bull for cattle ranching.
B
Cattle ranching is not a good source of income.
This is unsupported because even though ostrich farming may yield greater returns than cattle farming (relative statement), cattle farming could still be a good source of income (absolute statement).
C
A cow consumes no more feed than an ostrich does.
This is unsupported because the stimulus never clearly tells us how much cattle and ostriches need to eat.
D
The average ostrich farm generates almost five times as much profit as the average cattle ranch.
This is unsupported because while ostrich farming could potentially yield five times that of cattle ranching, we don’t know that the average ostrich farm is productive enough to reach these maximum possible gains.
E
Ostrich farmers typically lose money during their first year.
This is unsupported because although the startup costs are higher for ostrich farming than cattle farming, it is possible that both are profitable in their first year.