Question Type: Necessary Assumption

Task:
Which answer choice, if false, most weakens the argument

ARGUMENT CORE

conclusion
Drinking tea boosted people's immune system

evidence
In a study, people who only drank tea took 1/2 as long to respond to germs as did people who only drank coffee

ANALYSIS

Since our goal with the correct answer is to negate it and see if it would weaken the argument, we should think through how we could debate this author.

"How could we argue that tea did NOT boost their immune defenses?"

With any study where we're comparing two groups based on some experimental variable (tea vs. coffee), we have to ask the underlying questions of any good science experiment:

Were these groups equivalent, other than which drink they had? Were there any differences between the tea and coffee group in terms of initial health / age / fitness / history of drinking tea vs. coffee, etc.?

In order to judge the "1/2 as long response time" as a direct effect of tea vs. coffee, we have to control for all these other variables.


ANSWER CHOICES

(A) If some participants drank tea AND coffee, would that give us a way to argue that tea didn't boost the immune system?

No. The study may have had lots of different groups: tea only, coffee only, tea+coffee, neither. No matter what, there WAS a tea only group and there WAS a coffee only group, and there WAS a significant difference between them in immune response time.

(B) If coffee DOES have other health benefits, does that let us argue that tea didn't boost the immune system? Definitely not.

(C) If coffee DID cause blood cell response time to double, does that let us argue that tea didn't boost the immune system? Hmmm. It's weirdly mathy. Drinking coffee meant cell response time was twice as fast as normal. Drinking tea was 1/2 as long as coffee. So drinking tea was normal response time. Oh! So drinking tea did NOT boost the immune response. The tea-only group just had a normal response time.

(D) This looks like the sort of study-shenanigans we were thinking about before. But this is about coffee drinkers and tea drinkers in general, and the conclusion is just about the study participants' (we don't even know if they WERE coffee/tea drinkers to begin with)

(E) Extreme alert. "ANY chemicals"? If coffee and tea DO have at least one disease-fighting chemical in common, does that help me argue that drinking tea did NOT boost immune response time? Definitely not.

The correct answer is (C).

KUDOS will be appreciated

I chose answer A, because I thought that A eliminates possibilities that other factors were involved that could have affected the study. Can anyone clarify how A could be eliminated?

IMO, A is already stated in the argument.

As a general question....can practice on LSAT question help in gmat CR?

Mansoor50, yes. And bumping for further discussion.
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A recent study showed that the immune system blood cells of the study's participants who drank tea but no coffee took half as long to respond to germs as did the blood cells of participants who drank coffee but no tea. Thus, drinking tea boosted the participants' immune system defenses.

Which one of the following is an assumption on which the argument depends?

.(A)  All of the participants in the study drank either tea or coffee, and none drank both.

.(B)  Coffee has no health benefits that are as valuable as the boost that tea purportedly gives to the body's immune system.

.(C)  In the study, drinking coffee did not cause the blood cell response time to double.

.(D)  Coffee drinkers in general are no more likely to exercise and eat healthily than are tea drinkers.

.(E)  Coffee and tea do not have in common any chemicals that fight disease in the human body

One may think of a possible assumption that blood cell response time in participants who drank tea didn't halved but if that is so then the question would have been easy. On the contrary, C says the opposite of above, making it difficult to answer.
Only A and C look good but A loses for considering participants who may/may not have drank both i.e. increasing the scope of participants of experiment.

Answer C.
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