A recent study showed that the immune system blood cells of the study's participants who drank tea but no coffee took...

Ryan-Mahabir on October 22, 2019

Why is C correct? Why is D incorrect?


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AndreaK on October 23, 2019

Hi @ryan-mahabir,

Good question. C is correct because if in the study drinking coffee caused the blood cell response time to double, it casts some serious doubt on the plausibility of the conclusion. So the argument is relying on the fact that the situation described in C didn’t take place, which makes it a necessary assumption of the argument.

For D, likelihood to exercise or eat healthy on the part of coffee drinkers doesn’t have any effect on our conclusion. “Drinking tea boosted participants’ immune system defenses” isn’t relying on the truth of that information.

Hope this helps!

tomgbean on December 6, 2019

But even if the blood cell time doubled for coffee drinkers, doesn't that strengthen the conclusion because coffee would actually impede the immune system? I thought were were suppose to look for answer choices whose contrapositive would destroy the conclusion?

shunhe on December 23, 2019


Let's say the blood cell time did double for coffee drinkers, and the normal blood cell response time is 5 seconds. Then coffee drinkers will have 10 second response times. Then even if tea-only drinkers took half as long, or 5 seconds, then drinking the tea didn't boost their immune system defenses, since they still have the same response time as normal people. Hope this helps!

NAM1921 on April 27, 2023

Yes ok thanks this really helps!