PrepTest 152, Section 2, Question 11
Last year the Lalolah River was ranked by(46 more words not shown)
The reasoning in the argument(5 more words not shown)
- Ainterprets lack of(10 more words not shown)
- Brelies on an(6 more words not shown)
- Cdoes not disclose(6 more words not shown)
- Dconfuses the state(17 more words not shown)
- Eequates a decrease(10 more words not shown)
Reading the argument
What if the other rivers got dirtier?
Being the most polluted river tells us where Lalolah stands in the group, not exactly how polluted it is. All fifteen rivers could be relatively clean or extremely dirty. The ranking alone doesn't settle that.
Now Lalolah has dropped from first to third in pollution. Imagine it had 100 units of pollution last year, with the next two rivers at 90 and 80. If those two rise to 120 and 110 while Lalolah stays at 100, Lalolah becomes third without getting any cleaner. Those are invented numbers, but they show how the reported change can occur without a successful cleanup.
What we’re looking for
For the flaw, I'd look for confusing a better position in the ranking with a reduction in Lalolah's own pollution. The cleanup might be working, but this comparison doesn't establish that it is.
Working the answers
- A
The author has evidence: Lalolah's changed ranking. The mistake is what the ranking is taken to show, not treating the absence of evidence for one claim as evidence for its opposite. We can accept the ranking and still reject the inference.
- B
'Most polluted' keeps the same comparative meaning throughout. We don't need the phrase to shift meaning for the conclusion to fail. Two other rivers getting worse could explain the change even if the ranking uses a perfectly clear and consistent standard.
- C
More information about how pollution is measured wouldn't fix this problem by itself. Even an accurate ranking can change because the other rivers deteriorate. Our example accepts the rankings as correct and still leaves Lalolah no cleaner, so the flaw isn't simply the omission of a ranking method.
- D
The conclusion concerns cleanup measures for Lalolah. It doesn't conclude that the entire water district became cleaner. The mistake compares one river with the others; it doesn't transfer a property of individual rivers to the district as a whole.
- ECorrect
Lalolah improved relative to the other ranked rivers, but that doesn't show an absolute decrease in its pollution. 'Absolute' here means a change in Lalolah itself, rather than a change in where it stands compared with its neighbors. The river could remain just as polluted—or even become more polluted—while two others pass it. The author needs evidence of Lalolah getting cleaner, not merely slipping down the list of the dirtiest rivers.
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