PrepTest 141, Section 4, Question 17
A positive correlation has been found between the(53 more words not shown)
Which one of the following(7 more words not shown)
- AIn cities where(42 more words not shown)
- BIf the ailment(26 more words not shown)
- CIn each of(32 more words not shown)
- DIf high concentrations(38 more words not shown)
- EIn cities in(30 more words not shown)
Reading the argument
Other pollutants might explain the illness. That doesn't clear soot of responsibility.
The author notices that soot and the ailment occur together, then points out that the same cities usually have other air pollutants too. Fair enough: those other pollutants deserve investigation. But why conclude that soot probably isn't a cause? Soot could still contribute, even if something else contributes as well.
What we’re looking for
To weaken this argument, I'd first think of removing soot while leaving the other conditions comparable. If the illness became much less frequent, that would give us evidence against dismissing soot. The point wouldn't be to declare the cause settled beyond doubt. It would be to show that the author has too quickly blamed the other pollutants and set soot aside.
Working the answers
- A
This starts with the comparison I wanted, but the result goes the wrong way. These cities have little or no soot and still have just as much illness. That doesn't prove soot can never contribute, but it makes other pollutants look more plausible as an explanation. It doesn't challenge the author's dismissal of soot in the way a drop in illness would.
- B
The conditional rule would help if the ailment rarely occurred outside high-soot cities. But we haven't established that condition. A positive correlation doesn't mean the illness is rare everywhere else. We cannot apply the rule merely because its conclusion is what a weakener would support.
- CCorrect
This uses the other useful comparison: plenty of soot, but little of the other air pollution. The illness is still at least as frequent as anywhere else. That undercuts the author's suggestion that the other pollutants are a reason to dismiss soot. The alternative pollution is largely absent, yet the ailment remains especially common. C doesn't prove soot is the cause, but it gives a concrete reason to question the argument's explanation.
- D
Multiple pollutants could each contribute, and soot could conceivably be among them. But D only says that multiple causes are possible; it doesn't identify soot as one of them or give evidence that soot contributes. C does much more by supplying actual cities where the proposed alternative pollutants are scarce and the ailment remains common.
- E
This introduces still more plausible alternative causes, such as pollution outside the air. That gives the author additional grounds for questioning whether the soot correlation identifies the cause. It doesn't provide the evidence for a role for soot that would most weaken the argument.
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