Which of the following, if true, would make the information

In 1996, scientists caused an experimental flood of the Colorado River by releasing water from Glen Canyon Dam above the Grand Canyon. Because an unintentional flood in 1983 had reduced the river’s introduced population of nonnative trout, biologists were concerned that the experimental flood would wash many fish, native and nonnative,downstream. To find out, biologists placed nets in the river. The nets captured a few more trout than they would have without the flood but did not show substantial flushing of native fish, whose ancestors had, after all, survived many larger natural floods. The biologists surmised that the native species(and most of the trout) must have quickly retreated to protected areas along the riverbank.

Which of the following, if true, would make the information presented in the passage compatible with the experimental flood’s in fact having caused substantial flushing of native fish?

  1. Many of the native fish are too small to have, been captured by the nets.
  2. There had been an increase from normal levels in the native fish population prior to the flood.
  3. The native fish in the Colorado are much stronger swimmers than taxonomically similar fish in other rivers in the region.
  4. The unintentional flood of 1983 had not affected the river’s trout population as much as was originally thought.
  5. The experimental flood raised the water level much less than a typical natural flood would have.

An important thing to keep in mind about the Reading Comprehension section of the GRE as we use PowerPrep online to study is that it is just that—reading comprehension. In other words, as difficult as it may seem, and it can be pretty tricky, the test makers will always give us all the information we need in the passage to answer the question. Even questions in which our answers come from outside of the passage, like question 18 of the second Verbal section on practice test 1, abide by this rule.

This question is actually a familiar type, though it hides behind some phrasing specific to the passage. We should note, however, that it includes the phrase “if true,” which generally means we’re looking for an answer that either supports a conclusion drawn by the passage, or else weakens that conclusion. In this case, we’re asked what answer would “be compatible” with a conclusion provided in the question itself: the experimental flood’s in fact having caused substantial flooding of native fish. So, our first order of business is to determine how the experiment arrived at the conclusion that the flood did not flush native fish (even if we don’t remember that this was the conclusion from the passage, the phrase “in fact” implies that that passage arrived at a different conclusion).

Alright, so this experimental flood that happened in 1996 was done by releasing water from a dam in order to simulate an actual flood that happened in 1983 that reduced the trout population. The scientists thought this might flush both native AND nonnative fish downstream. Aha! The third sentence tells us that in order to test their theory, they placed nets in the river, and, according to the next sentence, they arrived at the conclusion that the flood did not flush out native species because the nets didn’t catch many native fish. According to the last sentence, the scientists believe the reason for this is that the native fish were smart enough to retreat to protected areas.

So, we’re looking for an answer that might suggest that the experiment wasn’t exactly perfect. We know that the scientists based their conclusion on what fish were caught in their nets, so our answer will likely have something to do with this method.

  • Many of the native fish are too small to have, been captured by the nets.

Mmmhmmm! This answer sounds just like what we predicted a good answer would sound like. It suggests that the nets would not have caught the native fish because they are too small. If this is the case, then the scientists’ experiment wouldn’t actually be very conclusive since their findings were based on the lack of native fish caught in the nets. We should keep A, but let’s scope out the other answers in case we’re missing something.

  • There had been an increase from normal levels in the native fish population prior to the flood.

This answer might make sense if the findings were based on counting the number of native fish sometime before and sometime after the flood, but it was heavily implied (nearly directly stated) that the findings regarding native fish were based on the lack of native fish caught in nets after the flood. We do not know whether or not scientists had counted or estimated populations before and after the flood, so this answer is irrelevant. We can eliminate B.

  • The native fish in the Colorado are much stronger swimmers than taxonomically similar fish in other rivers in the region.

One thing we want to keep an eye out for in this type of question is irrelevant information. Since our answer won’t be directly found in the passage, it’s easy for the test makers to slip in information that doesn’t matter but sounds good (we can’t say “wait that wasn’t in the passage” because none of our answers actually were, even the correct one). Still, a comparison between fish native to this river and fish native to other rivers has nothing to do with whether or not native fish were flushed out during the experimental flood. This answer could challenge the scientists reasoning behind why native fish were not flushed out (being stronger swimmers could be an alternative to finding protected areas), but we aren’t trying to challenge that reasoning. We can eliminate C.

  • The unintentional flood of 1983 had not affected the river’s trout population as much as was originally thought.

This answer has nothing to do with native fish or the experimental flood, which should be a red flag. Still, it might be tempting to think that if one part of the passage is wrong more information could be incorrect, but the findings of the experimental flood were not based on observations made in the unintentional flood. We can eliminate D.

  • The experimental flood raised the water level much less than a typical natural flood would have.

Our question only asks about the experimental flood, not natural floods. Also this answer has nothing to do with native fish. We can eliminate E because it doesn’t challenge the findings of the experiment.

Turns out we were right! A is the only answer that suggests that there was a problem with the methods used to attain the results relevant to the question. A is correct.

 

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