PrepTest 156, Section 4, Question 12
Ecologist: El Niño, a global weather phenomenon that(59 more words not shown)
Which one of the following,(8 more words not shown)
- AIn region T,(13 more words not shown)
- BRodent populations in(14 more words not shown)
- CIn many regions(24 more words not shown)
- DIn region T,(17 more words not shown)
- EThe global warming(24 more words not shown)
Reading the argument
Heavy rain doesn't necessarily mean rain that lasts a long time.
The ecologist's chain initially sounds sensible: more El Niño events will bring heavy winter rainfall to region T, and long periods of sustained rain tend to bring more rodents. But those are two different descriptions of rain. What if an enormous amount falls during one week, followed by months without it? That could make the winter very wet overall without giving the rodents a long stretch of sustained rain.
I also wonder whether the season matters. Perhaps rain during winter doesn't help the rodents in the same way as rain during their breeding season. We aren't given that information, so it's another possibility rather than an established objection.
What we’re looking for
The weakening question asks for evidence against the predicted population increase. My strongest guess is a fact showing that El Niño's heavy rain isn't the kind of rain associated with more rodents. In particular, I'd look for a difference between how much falls and how long it keeps falling.
Working the answers
- A
A difference between summer and winter rainfall doesn't tell us whether El Niño will produce the sustained rain associated with rodent increases. Winter could be wetter than summer either way. We need evidence against the predicted chain of effects, not just a seasonal comparison.
- B
Fewer rodents during stretches without heavy rain doesn't challenge the prediction about more heavy winter rain. If anything, that pattern is consistent with the ecologist's general thought that wetter conditions can support more rodents. It doesn't expose the gap between heavy rain and sustained rain.
- C
This is worth considering: some wetter places have fewer rodents. But comparing different regions leaves many other differences uncontrolled. Those places could differ in habitat, predators, or many other ways. Their smaller rodent populations don't tell us what increased rain will do within region T. D addresses the ecologist's actual chain much more directly.
- DCorrect
Wet winters in region T usually haven't involved long periods of sustained rain. That directly challenges the step we questioned. The ecologist expects heavy winter rainfall, but the population-increase evidence concerns sustained rainfall. If the first usually doesn't bring the second, the predicted increase loses its support. The answer needn't establish that the rodent population will fall; undermining the reason to expect a rise is enough.
- E
Other effects on rodents could matter, but in which direction? Those effects might decrease rodent populations, increase them, or offset one another. E never tells us. It raises the possibility of other influences without giving us a reason to think they work against the ecologist's prediction.
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