BTW, not sure if you know, but Dan is also a Bruin (law school) —
You are definitely right to say that the answer is commonly not predictable for weaken q’s —
One thing you mentioned was that you didn’t have as clear an understanding of the flaw when trying the problem in real-time. I think being able to see the flaw correctly really is your best tool for evaluating the relevancy of answer choices, so, whenever you are in a situation where you are finding the flaw difficult to see, you should feel less pressure to move on to the answer choices, and more pressure to really try and nail the reasoning issues.
BTW, this argument has a fairly common underlying structure:
Group A and Group B got similar results on a test of Issue X.
Therefore, Issue Y does not impact the broader group, Group C.
So, we know going in that the argument is indeed flawed, and we need to think about why — there are three main ways this type of structure could have problems —
1) Group A and Group B may not be good samples for Group C. For example, maybe for a question they sample the executives at a company then use that to generalize about the company as a whole.
2) The issue in the premise is different than the issue in the conclusion. Maybe they talk about one type of injury in the premises and a different (more general, more specific, or just different) type of injury in the conclusion.
3) Group A and Group B have differences that throw off the comparison.
For this specific problem, notice we don’t really have concerns 1 or 2 — the premises are about a large group of joggers, and the conclusion is about joggers; the premises are about getting injuries, and the conclusion is about getting injuries.
And so the most suspicious weak link is that perhaps there are differences between Group A and Group B that throw off the comparison.
Per what you wrote, and I could be wrong, it seems like you pretty much got to this same point —
In any case, going into the answer choices, if that’s your understanding of the flaw, then what you are looking for is a potential explanation that tells us Group A and Group B (in this case joggers who stretch vs those who don’t) are not comparable in a relevant way (in this case, the amount of injury they tend to sustain) —
Looking at the answers from that perspective, I think (D) jumps out as being a bit more obvious.
Not sure if the above helps, but thought reading through it might make something click for you —
Another comment I have is that often strengthen / weaken right answers don’t give off that “slam dunk” sort of feeling you might get from, say, a Sufficient Assumption or ID the Conclusion q, where there are much more absolute ways to gauge correctness. That’s another reason they can feel more difficult, and it’s a reason why elimination skills are very important for these problems.
You mentioned you sometimes get wrong q’s you felt certain you got right, and I also get the sense that you feel you dismissed the eventual right answer here a bit too easily at first — make sure to keep working on your elimination process — you want to develop a stronger and stronger sense of when you feel certain that an answer must absolutely be incorrect, and, otherwise, you want to not eliminate those answers that, at first glance, don’t seem right, but, that, regardless, you can’t find an explicit reason to get rid of. Think of eliminating what turns out to eventually be the right answer the worst of all LR sins, and try to be hyper critical every time it happens.
Ended up writing more than I planned (as always) — sorry about that — in any case, please feel free to use what helps and to also ignore whatever doesn’t apply to you — you know yourself best — but hope that helps —