Critical Reasoning

The male sage grouse has air sacs that when not inflated, lie hidden beneath the grouse’s neck feathers. During its spring courtship ritual, the male sage grouse inflates these air sacs and displays them to the female sage grouse. Some scientists hypothesize that this courtship ritual serves as a means for female sage grouse to select healthy mates.
Which one of the following, if true, most strongly supports the scientists’ hypothesis?
(A) Some female sage grouse mate with unhealthy male sage grouse.
(B) When diseased male sage grouse were treated with antibiotics, they were not selected by female sage grouse during the courtship ritual.
(C) Some healthy male sages grouse do not inflate their air sacs as part of the courtship ritual.
(D) Male sage grouse are prone to parasitic infections that exhibit symptoms visible on the birds’ air sacs.
(E) The sage grouse is commonly afflicted with a strain of malaria that tends to change as the organism that causes it undergoes mutation.

D

Male sage grouse are prone to parasitic infections that exhibit symptoms visible on the birds’ air sacs.


shows the link

D is not mentioned.

IMO:C

OA?

NSNguyen wrote:The male sage grouse has air sacs that when not inflated, lie hidden beneath the grouse’s neck feathers. During its spring courtship ritual, the male sage grouse inflates these air sacs and displays them to the female sage grouse. Some scientists hypothesize that this courtship ritual serves as a means for female sage grouse to select healthy mates.
Which one of the following, if true, most strongly supports the scientists’ hypothesis?
(A) Some female sage grouse mate with unhealthy male sage grouse.
(B) When diseased male sage grouse were treated with antibiotics, they were not selected by female sage grouse during the courtship ritual.
(C) Some healthy male sages grouse do not inflate their air sacs as part of the courtship ritual.
(D) Male sage grouse are prone to parasitic infections that exhibit symptoms visible on the birds’ air sacs.
(E) The sage grouse is commonly afflicted with a strain of malaria that tends to change as the organism that causes it undergoes mutation.

"Support a hypothesis" means we want to strengthen the scientists' argument.

Let's break this argument down:

conc: ritual allows females to select healthy mates

evid: males inflate their usually hidden air sacs during the rituals.

To strengthen an argument, we often back up the author's central assumption. Of course to do so, we need to identify that assumption.

The classic Kaplan method for identifying assumptions is to start with the conclusion and ask yourself "is there anything mentioned in the conclusion that we have no evidence about at all?" We can't draw a conclusion with no support, so if there is such a new term, then the author must be making an assumption about it.

Next, look at the evidence and ask yourself a similar question: "Is there anything mentioned in the evidence that's connected neither to another piece of evidence nor the conclusion?"

Applying the method to this question almost makes it trivial!

In the conclusion, we read about "healthy mates" for the first time.
In the evidence, the scientists focus not on health, but on inflated air sacs.

So, our prediction for the central assumption: "there must be a connection between inflated air sacs and judging health".

Since we're looking at a strengthening question, we predict that the correct answer will back up the assumption. If this were a weakener, we'd look for a choice that attacks the assumption. If this were an assumption question, we'd simply look for a choice that paraphrases the assumption.

(D) gives us exactly what we predict - a health issue that's visible on the air sacs. In fact, at a very aggressive glance (once you've taken the time to make a prediction, you want to be ultra aggressive when you look at the choices), only (c) and (d) mention the two things we're looking for, so we wouldn't even think about (a), (b) or (e).

We eliminate (c) because "some" is a very weak word ("some" literally means "at least one" in the GMAT world) and because it doesn't tell us what unhealthy male sage grouse do, so we have no clue how it impacts the argument.

Excellent explanation Stuart. I picked D too because Female birds can decide whether a male bird is health or not depending on the visible symptoms.

Indeed!!An Excellent explanation Stuart!!

Even i went by the same rule which is also mentioned in CR Bible.
I also found " healthy mates" as the new term and thats why choose C.

Can you please tell me in which Kaplan book this strategy is given.

I have read Kaplan but have not come across such strategy( read only in Cr bible).I have Kaplan verbal workbook.

Thanks again.

raunekk wrote:Indeed!!An Excellent explanation Stuart!!

Even i went by the same rule which is also mentioned in CR Bible.
I also found " healthy mates" as the new term and thats why choose C.

Can you please tell me in which Kaplan book this strategy is given.

I have read Kaplan but have not come across such strategy( read only in Cr bible).I have Kaplan verbal workbook.

Thanks again.

I'll check the books when I'm in the office over the weekend and let you know!

Many thanks to Stuart Kovinsky
smart explaination

Stuart Kovinsky wrote:We eliminate (c) because "some" is a very weak word ("some" literally means "at least one" in the GMAT world) and because it doesn't tell us what unhealthy male sage grouse do, so we have no clue how it impacts the argument.

Stuart,

I thought words which are too specific and unequivocal are generally wrong when compared to vauge and general words, like answers usign workds like may, perhaps etc? Is it true or it's a myth? Or, is it generally true only for Inference questions on the RC section? Your input is really appreciated.

ildude02 wrote:

Stuart Kovinsky wrote:We eliminate (c) because "some" is a very weak word ("some" literally means "at least one" in the GMAT world) and because it doesn't tell us what unhealthy male sage grouse do, so we have no clue how it impacts the argument.

Stuart,

I thought words which are too specific and unequivocal are generally wrong when compared to vauge and general words, like answers usign workds like may, perhaps etc? Is it true or it's a myth? Or, is it generally true only for Inference questions on the RC section? Your input is really appreciated.

That distinction is most important for assumption and inference questions.

In both cases, it's very rare for an extremely worded answer choice to be correct. In general, avoid words like "all", "never", "always" and so on. The only exception to that rule is if the argument/stimulus itself uses extreme language, which is rare on the GMAT.

Thanks for your response.

Than you stuart

your explanation of "new term" in conclusion is great.

This is mentioned in Kaplan Book. In CR Bible this is mentioned as "supporter assumption"

CR bible also mention "defender assumption" , Stuart, pls, give us an example of "defender assumption". I wish to know of your explanation of this . pls, Stuart.

duongthang wrote:Than you stuart

your explanation of "new term" in conclusion is great.

This is mentioned in Kaplan Book. In CR Bible this is mentioned as "supporter assumption"

CR bible also mention "defender assumption" , Stuart, pls, give us an example of "defender assumption". I wish to know of your explanation of this . pls, Stuart.

Hi,

I'm not familiar with the term, sorry.

An assumption is, by definition, something that must be true in order for the conclusion to be true. On the LSAT we often differentiate between necessary and sufficient assumptions, because there are two different types of assumption questions on that exam, but there's no need to make that distinction for the GMAT.

I am leaning more towards C, but I'm not sure about it.