PrepTest 128, Section 2, Question 20
Geologist: A new method for forecasting earthquakes has(63 more words not shown)
Which one of the following,(10 more words not shown)
- AEven if an(26 more words not shown)
- BAn earthquake-forecasting method(22 more words not shown)
- CAn earthquake-forecasting method(20 more words not shown)
- DSeveral well-established methods(19 more words not shown)
- EAn earthquake-forecasting technique,(28 more words not shown)
Reading the argument
The method has reliably predicted several earthquakes. That is promising, though it doesn't establish how it performs in every circumstance. Its limitation is that a prediction spans two and a half points on the Richter scale, potentially covering both a barely noticeable quake and a damaging one.
Could that still help? If older methods gave a five-point range, narrowing the forecast to two and a half points might be progress. Even an imprecise warning could let people prepare or move to a safer place. Imperfect information isn't automatically useless.
What we’re looking for
My first question is how this method compares with the alternatives. But the task is stronger than simply finding a reason to doubt its value: we need an assumption that makes the conclusion follow. The answer must connect this method's stated limitation to its being unlikely to be useful.
Working the answers
- A
This requires reliable predictions for likely usefulness. But the argument doesn't establish that the new method is unreliable; it says the forecasts are imprecise about magnitude. A prediction can reliably place a quake within a broad range without distinguishing how damaging it will be. A doesn't connect that known limitation to the conclusion.
- BCorrect
B makes always distinguishing barely noticeable earthquakes from substantially destructive ones a requirement for likely usefulness. The passage tells us the new method's range can straddle that distinction. It therefore fails B's requirement, and the conclusion follows: it is unlikely to be useful. 'Barely noticeable' matches 'marginally perceptible,' and 'substantial destruction' matches the contrast with considerable damage.
- C
Not having been shown useful is different from being unlikely to be useful. A new method might be promising before a large body of results is available. C concerns the amount of evidence required to establish usefulness; it doesn't establish the geologist's negative prediction from the stated lack of precision.
- D
This speaks to my initial question about better alternatives, but it doesn't prove that the new method lacks likely usefulness. Perhaps the more precise methods work only in winter while the new method works all year. It could then provide valuable warnings when the older methods cannot. Greater precision elsewhere doesn't by itself eliminate this method's usefulness.
- E
'Never distinguish' is much stronger than 'not always distinguish.' A two-and-a-half-point range could sometimes fall entirely among small quakes or entirely among destructive ones; other times it could span both. The passage doesn't establish that the method never distinguishes the relevant categories, so we cannot apply E's rule. B works because it requires success every time, and the stated limitation shows that requirement is not met.
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