What we have here is a "strengthen the conclusion" question. To strengthen a conclusion, you need to make one of the argument's underlying assumptions into a supporting premise by stating it explicitly. This argument is essentially:

1. Crowding leads to aggression in rats.
2. However, crowding does NOT lead to aggression in rhesus monkeys.
3. Therefore, crowding probably does NOT lead to aggression in monkeys the way it does in rats.

Statements 1 and 2 are premises. Statement 3 is our conclusion. The question you want to ask yourself is: "What assumption are they making in between statements 2 and 3?" That assumption is going to be the answer to this type of question.

In this example, you can't assume that the behavior of Rhesus monkeys would reflect the behavior of other monkeys. Although we could probably justify this statement if we watch a lot of Discovery Channel, we can't use that external knowledge on the GMAT. Answer choice C is a version of this assumption; it makes explicit the fact that rhesus monkeys are actually more aggressive than other monkeys. The natural next step of this chain of logic is that if crowding doesn't make rhesus monkeys act aggressively, it probably doesn't make any other monkeys act aggressively.

As a result, C is the best way to strengthen this conclusion. Hope that's helpful!

Brett
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Brett Beach-Kimball | Manhattan GMAT Instructor

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(C) definately makes sense and strengthen the argument. But I am wondering that (A) also strengthens the argument by saying that all the "cpoing" behaviours are found among rhesus monkeys living in uncrowded conditions. Because if that is not the case, it simply means that the attacking nature has got increased.

@Brett, can you please through some light on this?

syog,

(A) gives us more information about rhesus monkeys: In crowded conditions, they cope in specific ways other than becoming aggressive. However, this only helps us better understand this particular species of monkey. We still have no idea whether this species is typical.

The goal with strengthening the conclusion questions is to understand which does the MOST to strengthen the conclusion. With (C) we can clearly see the strengthening. With (A) we have to tell ourselves a story to strengthen the argument: "Rhesus monkeys don't show aggression. They don't show aggression because they have other ways of coping, such as acting submissive. Since the rhesus monkey has an alternative to aggression, other monkeys probably do also."

Notice how this "story" we have to tell ourselves contains its own assumptions that still need to be overcome. Thus, although (A) might strengthen a bit, it doesn't strengthen the most.

Does that help?

Brett
_________________

Brett Beach-Kimball | Manhattan GMAT Instructor

Manhattan GMAT Discount | Manhattan GMAT Reviews