PrepTest 145, Section 2, Question 10
One year ago, a municipality banned dishwasher detergents(48 more words not shown)
The answer to which one(12 more words not shown)
- AWhy did many(7 more words not shown)
- BWhat pollutants, if(7 more words not shown)
- CWere any changes(15 more words not shown)
- DDoes most of(16 more words not shown)
- EDid municipal officials(12 more words not shown)
Reading the argument
Less phosphate leaving the treatment plant doesn't tell us, by itself, what people bought.
Maybe residents used less detergent without switching to a phosphate-free version. Or perhaps the detergent still contained phosphates, but in a lower concentration—say, 20 percent instead of 50 percent. Either change could reduce the pollution even if nobody made the switch the author claims.
What if the treatment plant got better at removing phosphates? The same amount could arrive at the plant, but less would leave it. Then the improvement would reflect treatment, not a change in residents' shopping.
What we’re looking for
We're asked which question would help evaluate the argument. A useful question should help us distinguish the author's explanation from an alternative like these. We want to know whether the drop at the plant really provides evidence that some residents switched to phosphate-free detergent.
Working the answers
- A
Residents might keep using their old detergent because of price, habit, or preference. Their reasons don't establish whether anyone else switched. The argument acknowledges continued phosphate use; it claims that some people nevertheless changed products. Asking about the continuing users' motives doesn't test that inference.
- B
Phosphate-free detergent might contain other pollutants and still be phosphate-free. This question would help assess its broader environmental effects, but our conclusion is about whether residents switched to it. Whether the new products are entirely clean is a separate issue.
- CCorrect
If the plant adopted a method that removes more phosphates, the lower pollution could result from better treatment even with the same detergent use. That answer would weaken the inference about consumers. If treatment remained unchanged, that particular alternative would lose its basis.
An unchanged process wouldn't prove that residents switched; reduced use or a change in detergent concentration could still matter. But the answer would resolve one concrete doubt about what the pollution figures mean. That's why this is a useful question for evaluating the argument.
- D
This asks how much of the waterways' phosphate pollution comes from this plant. Whether the plant contributes most of it or a small share, we still need to explain the decrease in pollution from the plant itself. Its share of total pollution doesn't tell us whether residents changed detergents.
- E
Trying to block out-of-town purchases doesn't tell us whether officials succeeded or whether anyone switched products. An enforcement attempt could fail completely. C more directly tests what caused the observed change at the plant, which is the evidence the argument uses.
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