The key issue here, as the comments indicate, is figuring out how answer choice B doesn't contradict/attack the premise.

The premise, properly understood, is: The research indicates(result). Attacking the premise, would call into question the research itself. Saying that the research didn't show what the scientist says it shows (e.g., "The research was unable to differentiate the impulsive behavior from other behavior.") Instead, AC B goes: Ok sure the research does indicate that, but you can't make this correlation because you can't isolate the behavior. 

This is so subtle that on the actual LSAT you'd be better off PoE the rest and choosing this assuming it doesn't attack the premise in some subtle way. Because the rest of the ACs don't work (I say with hindsight).

The challenge of this question, and why it only works as an MSS, is two assumptions that would be a mistake on other question types:

1. Something that "helps people to get along with each other" is the same as social harmony.

2. Social harmony has beneficial effects for society.

Then we can setup a dialogue to pronounce this:

Tom: Etiquette helps people to get along with each other. It must have some beneficial effects for society.

Dave: No, etiquette does not have beneficial effects for society.

Tom: You say that, but you think social harmony is beneficial for society. 

What happened here? Now its easier to see that Tom (the author), points out that Dave (critic of etiquette) is saying you must not know (be mistaken) thatetiquette promotes a position you hold (social harmony is good). And the assumption we have to make for this MSS is that social harmony being good means it is benefical to society.

Thus, AC C says Dave, who doesn't know etiquette leads to social harmony (something he supports), doesn't know etiquette benefits society.

B is great AC to demonstrate the difference between NA/SA.

First, B is wrong because it flips sufficient-necessary. That is, the conclusion says: "Crows can recognize threatening people and pass concerns to other crows." Why? Because this shrieking and dive-bombing behavior seen in the experiment. For NA, we know that the correct AC feeds into the existing logic of the argument-- that being, "shrieking and dive-bombing --> recognize threat." But B says, "recognize threat --> shrieking and dive-bombing." A mistaken reversal.

But, let's say hypothetically, B was: "crows respond by shrieking and dive-bombing always when they perceive an individual as threatening" or "shrieking and dive-bombing --> recognize threat." A correct NA AC.

And if the conclusion was just "capable of recognizing threatening people" this AC would be both a SA and NA. Since this assumption would ensure the conclusion. But we still haven't met the conclusions' second criteria, "can even pass their concerns on to other crows." So, hypothetically, if this were a SA question, even with neccessary/sufficiency corrected in B, it would be wrong.

So what's the catch? The necessary assumption of shrieking and dive-bombing meaning recognizing threat, is just more obvious. And B plays on that. Meanwhile, AC A actually plays into a NA of the other part of the conclusion ("not all the same crows --> passing concerns").

I think like most people, I conflated the conclusion's "dug from the mine" as originating from the mine. Once you realize that difference, this AC is painfully obvious. I ruled out A because I thought "So what? Where they got it from doesn't mean it isn't from the mine."

This is one of those questions where, just with the conclusion, no premises or context, I would have been more likely to get this right than I was with the distractions.

This question is really good practice for recognizing the role of powerful/weak language, and the prescriptive/descriptive nature of the ACs. Sure, there are better ways to cross out some of these, but for the sake of practice, it's nice to notice.

A key part of the stimulus- Studies have shown: Of the set of schools that emphasize technology, these schools spend more time teaching computer skills than basic math and reading skills.

---> This is descriptive. It is saying what studies show about a specific subset of schools. There isn't really any strong language to speak of.

A: This is prescriptive. It is making a value judgment (literally says "valuable") with a comparative.

B: Ok this is descriptive, but it is strong (as others have noted). This AC says "cannot." The studies describe that balancing isn't occurring; it doesn't say it's impossible (cannot) to balance.

C: Prescriptive and very strong. It is saying X action is required to accomplish Y.

E: "Should" very quickly gives this away as prescriptive.

D (Correct AC): Weak ("can") and descriptive. Now, I know personally, two changes scared me: "recent educational developments" and "basic skills." These seem like assumptions. But when I go back to the stimulus, "Until fairly recently" allows for the first part, and "basic math and reading skills" means that math and reading sit inside a set of basic skills.

The difficulty of this question is that almost all the AC's have classic traps (including my own names):

A: Ad hominem. Attacking source of bias doesn't weaken argument.

B: "Excessive Assumptions" - You have to assume too much from too little. If you pick this, you try too hard to make ACs that don't work, work.

D: "Relevant to the Wrong Thing" - Irrelevant to conclusion, only relevant to premises.

E: "Common Sense =/= LSAT" - Says something that seems relevant and critical, but that something exists outside of strict logical thinking.

If you tempted/picked the following AC's consider this:

D: Start highlighting the conclusion (dioxin is unlikely to be the cause). D doesn't actually talk about dioxin as the cause, so it does nothing to the conclusion. 

B: You need to focus on how many assumptions you make with ACs. Assumptions: You need to assume the rate variance is severe (if its slow decomposition, a variance of 20 to 21 years is technically a variance) and that this river has the conditions in question that would make faster decomposition.

A: Basically attacking the source as biased (its an ad hominem) is never valid in the LSAT, anywhere.

E: So what? You don't need to understand everything to make a cause-and-effect. Example: I don't need to understand gravity to realize when I let go of something (cause) the thing will fall (effect).

For weaken in the ACs, when I'm really split I basically just count how many assumptions I need to make for an AC to weaken. Since the metric of "reasonable assumptions" can be hard to pinpoint, just going "oh wow I need to stack like 4 assumptions" reveals why answers don't work. Specifically, here's what how I got this right:

1. Ok so the conclusion (which I highlighted) is "dioxin is unlikely to be the cause."

2. I need something that undermines the premises that connect to this conclusion, which is the idea that it can't be dioxin from the mills since during the shutdowns fish recover but dioxin decomposes slowly, so they shouldn't recover.

3. Ok if I'm brutually honesty I had no prephrases here. The logic is weak but it could go any direction.

4. Use the PowerScore approach (only eliminate what you are confident about, don't waste tons of time completely considering "maybe" answers):

A: Its very rare (if ever?) the LSAT allows an attack of bias (ad hominem) to be a valid attack. But maybe? I move on.

B: For this to work I need to assume two huge things (among others): 1. This rate varies outside of the "very slowly" standard in the stimulus (like what if it can go from 20 years to 22 years based on condition? Thats still variance), 2. That the conditions in this river are the ones that make it fast. 2 huge assumptions. Move on for now.

C: Wait this works great: when the paper mills stop, the dioxin goes downstream within a few hours and the fish are no longer effected.

D: To quote JY "So what?" Nothing here ties back to the conclusion. The conclusion is that dioxin is not the cause, not that fish recover quickly from the hormonal changes. This one is a classic case where if you lose sight of the conclusion, it would make a lot more sense as the right AC. Luckily I noticed this: eliminate.

E: "Not thoroughly understood" doesn't disprove a causal relationship. This could just mean "Oh we don't know the molecular/chemical process that occurs for this to happen." Do I need to understand all the physics behind why when I push a wheelbarrow it goes forward to prove a cause-and-effect? Eliminate.

---

Ok now by not wasting time fully disproving every AC until I reached E, I'm left with just A, B, and C. C is clearly the strongest weaken left. I say strongest because I don't think it helps (at least for me) to try to categorically disprove A and B. Yes, the weaken questions only have one that actually weakens. And every prep service will remind you of this incessantly. But I think its better to just think about C as weakening the most.

@rkalam.21 There isn't directly. But my advise is if you go to drills and "select causal," a significant portion will be weaken/strengthen. I would say especially if you set them to 4/5 hard and then just keep drilling.

For the questions that pop up that aren't W/S, they'll still contain causal logic, so just take as much time on them to pick apart weaknesses (which is inverted to be strengths) as practice. (And still answer them ultimately so you don't waste them).

@ccd38148 Yeah you're completely right that the way I solved it would work for a SA question, me saying NA was a typo-- in fact, my example question stem is a SA question stem anyways.

In my experience, the way I've come to think of SA and NA as different is SA would be added into the chain to bridge the gap (here: "If you are a politician, then you are a member of the elite.") Whereas NA would have resolved this by feeding a definition into one of the existing elements (here: "Some politicians are elites.")

Idk if this distinction makes any sense, but in my head it does.

@mablevins08519 I know this was years ago, but I will answer this more fully for anyone else who trips up on this:

Original Stimulus Structure: We know that everyone refrains from littering (ERL) is sufficient because the sufficiency indicator "if," and the other part is necessary (Tanya refrains from littering, TRL). The argument then states that the sufficient condition is not met (except not really, this is the flaw, as it only applies to her friends, not everyone — FRL); therefore, the necessary one does not occur.

In Sum: ERL --> TRL | FRL --> TRL

AC D Structure: If/then introduces clear sufficiency necessary (whales need to surface for air = WSA, and easy to observe = EO). It then says that the necessary is met; therefore, the sufficient is met. This is a reversal without negation, so it is invalid. But this is not the flaw of the original. The original flaw is a part-to-whole error (conflates her friends with "everyone). It doesn't mix necessary with sufficient.

In Sum: WSA --> EO. | EO --> WSA.

This is all to say: The original error was treating everyone and Tanya's friends as the same (part-to-whole). D merely reverses necessary/sufficient, a different flaw.

Chaining Question 5 seems off to me. In my experience I think on the actual LSAT this would almost certainly be an intentional gap in the logic.

Where the stimulus would conclude: "When a society begins to decline, revolution will follow." The question stem might then be a NA with "The logic follows if which of the following is assumed:" And the right answer would require something to the effect of "That all politicians are elites."

What if in this society only the richest are considered elite (as we might say in much of the West), and many politicians are actually populist trying to fight the elite? To me that seems like much too strong of an inference, and the LSAT would never allow that.

This question really requires you to notice the difference between "GR advances" and just "GR." And from there to remember the basics of conditionals: necessary is required for the sufficient in the first place, but is not sufficient. In other words, funding alone of GR isn't sufficient for advances, but it is necessary-- you can't have GR advances WITHOUT GR and GR requires funding.

Also, "No" is being used in a different sense here than a negate necessary (group 4) indicator. In fact, I've noticed this is a common construction (i.e., "No x without Y"). The key indicator being "without" which is one of the synonyms of unless. Thus, we negate sufficient (group 3).

So, using the Unless Equation from PowerScore, which I find easier:

1. Make the word modified by "without" the necessary condition: "government or corporate funding."

2. Make the other part sufficient and negate it (it is already negative so it becomes positive): "ethical dilemmas resulting from advances in genetic research."

If/Then: If there are ethical dilemmas resulting from advances in genetic research, then there is government or corporate funding. (The AC is just the contrapositive of this).

From there, we know from the last sentence in the stimulus that this answer's necessary condition (funding) is also the necessary condition for any genetic research. And genetic research must logically be necessary for advances in genetic research. Not sufficient for advances, however, as B and E suggest.

I realize I made this unclear. To clarify:

*2. The other part is negated and becomes the sufficient.

The advantage is typically the non-modified term (the sufficient) is already negated, so negating it leads to all positives.

I found PowerScore's approach to Group 3 much easier (their so-called "Unless Equation). Avoid 7Sage's "picking either idea" approach, and instead give yourself a hard fast rule:

1. Whatever is modified by the indicator (i.e. unless, except, or without) is the necessary condition.

2. The other part becomes the sufficient.

Example: It will not rain unless Zeus is mad. (Zeus is modified by unless).

rain --> (zeus is mad)

Contrapositive: /(zeus is mad) --> /rain

This approach has the advantage of being similar to the real LSAT, where the modified term is typically negated, so you end up with all positives. And, as I said, it gives you a strict rule to guide your thinking.