Logical reasoning PrepTest 143 · Section 3 · Question 19

Incorrect. Studies can collect information from a wide variety of people and then use it to draw conclusions about a subset of those people. So this study might have been about beverages generally, and they pulled out the just-coffee and just-tea drinkers to compare them over this metric. There's no need for everyone in the study to fall exclusively into one of these two groups, so this answer is wrong.

Incorrect. The conclusion is just about immune system defenses, so other benefits are out of scope.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Coffee/~Tea Ð Immune system took twice as long as below group to respond to germs
Tea/~Coffee Ð Immune system took half as long as above group to respond to germs
Conclusion Ð Tea speeds up the immune system

Answer Anticipation:
This argument describes an observed phenomenon—differing rates of immune response in coffee and tea drinkers—and concludes an explanation for that phenomenon—tea speeds up immune response.

When an argument concludes one explanation for a phenomenon, it's assuming that no other explanations are true. For Strengthen with Necessary Premise arguments, then, the correct answer will frequently eliminate an alternative explanation.

Heading into the answers with that in mind would allow you to select the correct answer, but often, when another explanation is hinted at in the stimulus, it ends up being correct. Here, there's a perfectly viable explanation that's blatantly ignored—that coffee slows down the immune response. Since that's hinted at by the fact that the stimulus compares tea and coffee but then selects only to have an impact on an observed effect, it's likely that the correct answer will bring that up.

Answer Explanation:
This answer highlights a necessary assumption of the argument since it rules out an alternative explanation. The study noted that immune system response times were twice as long for coffee drinkers as tea drinkers, and it explained that difference by stating that the tea sped up the immune system. Based on this information, it's just as likely that the coffee slowed the immune system down. In order to reach this conclusion, that possibility must be ruled out, as this answer choice does.

Key Takeaway:
Phenomenon/explanation passages are assuming that no other explanation is correct, so correct answers in questions featuring this structure tend to deal in alternative explanations. If you can identify one that involves elements of the passage that don't feature in the concluded explanation, it's likely to be correct.

Incorrect. First, there's no indication that immune system response is related to diet or exercise. Second, even if there were, slight variations in the rates of these things in one group wouldn't necessarily explain a 2x difference in immune response—this answer is too strong in stating that it's "no more likely" one group does these things than the other.

Incorrect. They could have some chemicals in common that both help the body fight diseases, while also having different ones that alter the speed of that immune response, so this isn't necessary.