PrepTest 143, Section 3, Question 19
A recent study showed that the immune system(42 more words not shown)
Which one of the following(8 more words not shown)
- AAll of the(13 more words not shown)
- BCoffee has no(18 more words not shown)
- CIn the study,(12 more words not shown)
- DCoffee drinkers in(14 more words not shown)
- ECoffee and tea(14 more words not shown)
Reading the argument
Did tea help, or did coffee hurt?
Tea drinkers' blood cells responded in half the time taken by coffee drinkers' cells. That establishes a difference between the groups. It doesn't yet show what produced the difference.
Perhaps tea strengthens the immune response. Or perhaps coffee slows it down while tea does nothing. Another possibility is that the tea drinkers have healthier diets or habits, and those differences account for their faster response. We need more than a comparison to single out the drink as the cause.
What we’re looking for
The author credits tea. For an assumption that argument needs, I'd look for something ruling out an alternative explanation. We don't have to establish that tea is better for health in every respect; the question concerns this particular blood-cell response.
Working the answers
- A
The comparison uses people who drank tea but no coffee and people who drank coffee but no tea. The larger study could also include people who drank both or neither. Their existence wouldn't prevent the researchers from comparing these two groups, so A isn't required.
- B
Coffee could have other valuable health benefits while tea still improved this immune response. The argument isn't ranking the total health value of the two drinks. It doesn't need to establish that coffee lacks a benefit as valuable as tea's purported one.
- CCorrect
If coffee doubled the response time, it could produce the entire observed difference without tea improving anything. Imagine an unaffected response time of ten minutes. If tea leaves that at ten and coffee changes it to twenty, the tea group's time is half the coffee group's time, exactly as reported.
To use that comparison as evidence that tea boosted defenses, the author needs to rule out coffee producing the contrast in this way. C blocks that alternative. It doesn't rule out every possible difference between the groups, but it addresses one the argument cannot simply leave open.
- D
Watch the direction. Saying coffee drinkers are no more likely to exercise and eat healthily still allows tea drinkers to have healthier habits. That would leave our alternative explanation open. Nor does the argument need coffee drinkers to be no healthier: tea could improve this response even if coffee drinkers had some healthier habits. D doesn't supply the required protection against the competing explanation.
- E
The drinks could share a disease-fighting chemical and still differ in other ingredients or effects. Shared benefits don't establish that tea cannot provide an additional benefit to this response. The argument doesn't require the drinks to have no useful chemicals in common.
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