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.
According to the passage, which of the following is true of the Colorado River flood of 1983?
- The flood had a negative effect on the river’s trout population.
- There was substantial flushing of the river’s native fish population during the flood.
- Unlike the 1996 flood, it was not deliberately caused for scientific research purposes.
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. Questions that ask us about specific details of the text, such as question 19 of the second Verbal section on practice test 1, are a perfect example of this rule.
This question is about as straightforward as a question on the GRE can be; it simply asks what statements are true about a specific topic in the passage (the Colorado River flood of 1983) based on information in the passage. This is a select-all-that-apply question, though, so we’ll have to examine each choice individually in order to determine if it is something that is TRUE based on the passage. Also, since the question seems relatively easy, we’ll want to be sure to read EXTRA carefully, as it’s likely one or more of our answers may be a slight misinterpretation of the passage.
Let’s start by reviewing the information about the 1983 flood in the passage. This particular flood is actually only mentioned in one sentence of the passage. Since this question specifically asked what was true “according to the passage,” we also know that we’re looking for answers that can be found in the passage, so we don’t necessarily need to worry about if anything was implied or inferred about the flood elsewhere.
“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.”
While this is only one sentence, it does give us a few facts about the flood of 1983:
- It was unintentional (caused by mother nature, not scientists)
- It reduced nonnative trout populations
- It was the basis of a hypothesis concerning what the experimental flood would do to fish populations
This is pretty much the extent of what we’re told about the 1983 flood, so let’s see which answer(s) reflect these facts.
- The flood had a negative effect on the river’s trout population.
Did the trout population decrease? Indeed, it did, which would be defined as a “negative effect” as far as the trout population is concerned. Now, those of us who are chronic overthinkers may say “but trout are nonnative, couldn’t flushing out an invasive species be a good thing?” Well, we simply don’t know. We cannot assume that being nonnative fish makes trout undesirable (there are many invasive species that fit well into a habitat without changing its overall ecology too much), and also for the purposes of this answer it doesn’t matter. The “negative effect” simply describes an adverse effect on the population itself, so since there was a decline in trout, we can say that this answer is TRUE. Select answer A.
- There was substantial flushing of the river’s native fish population during the flood.
Well, we know that scientists hypothesized after this flood that an experimental flood my flush out native populations, but are we told that the 1983 flood actually flushed out native fish? The answer is NO! We are only told that the 1983 flood reduced nonnative trout populations and because of this scientists hypothesized the experimental flood my flush out both native and nonnative fish. We cannot assume that the 1983 flood ALSO flushed native fish. We should not select B.
- Unlike the 1996 flood, it was not deliberately caused for scientific research purposes.
We are told that the 1983 flood was “unintentional,” which means it was NOT deliberately caused by humans. C is TRUE and should be selected.
Questions like this one require carefully reading the passage to establish what is known about the keywords in the question and then carefully reading answers and taking them to mean exactly what they say in order to determine whether or not they are true based on the passage. If we rush or overthink things, we can make what is actually a fairly easy question difficult for ourselves. A and C are both correct.
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