Tagger wrote:
For years, Scientists have believed that a certain hormone produced by the human liver was triggered by enzyme U, which is released in the pancreas. Recently, however, researchers in Belgium discovered that Enzyme U is always preceded by the release of Enzyme W in the brain. Based on this, these researchers hypothesize that Enzyme W, not Enzyme U, triggers the production of the liver hormone.
If a second research project were set up to verify the findings of the Belgium researchers, which of the following test results most seriously weakens their hypothesis?
(A) Enzyme W is released, but not followed by the release of Enzyme U, although the liver hormone is produced.
(B) Enzyme U is released, but neither preceded by the release of Enzyme W, nor followed by the production of the liver hormone.
(C) Neither Enzyme W nor Enzyme U is released and the liver hormone is not produced.
(D) Enzyme W is released followed by the release of Enzyme U and the production of the liver hormone.
(E) Enzyme U is released and followed by the production of the liver hormone, although Enzyme W is not released.
KAPLAN OFFICIAL EXPLANATION:
Here's an example of a typical GMAT-style study. We're asked to find a set of results that would weaken a particular hypothesis, so the first thing to do is to locate and understand the hypothesis. It's tough to know at this point whether the weakener will simply offer some kind of proof against the hypothesis, or whether it will call attention to an assumption necessary for the hypothesis to hold. The Belgian researchers maintain that, since Enzyme U is always preceded by the release of Enzyme W, it must be Enzyme W, as opposed to U, that triggers the release of the liver hormone. Since the researchers argue that Enzyme W triggers the release of the liver hormone, in order to weaken this argument we can look for evidence either of another cause or of a situation in which the liver hormone appears in the presence of Enzyme U without Enzyme W.
Choice (E) directly counters the hypothesis by providing an example of the effect without the supposed cause. If the release of Enzyme U is followed by the production of the liver hormone, even though Enzyme W was not released, then that hammers the researchers' conclusion that Enzyme W is responsible for the hormone.
(A) strengthens, rather than weakens, the causal link between Enzyme W and production of the liver hormone. This choice provides an exact confirmation of what the researchers would predict.
(B) strengthens part of the hypothesis—the part that claims that Enzyme U does not trigger the production of the hormone—although it mentions nothing about W. It also contradicts the notion that U is always preceded by W, but does nothing to weaken the major hypothesis that W triggers the liver hormone.
(C) is perfectly consistent with the hypothesis: Without W, the researchers would not expect the liver hormone to be produced.
An 800 test taker can recognize statements that are perfectly consistent with a set of facts.
(D) represents exactly what we'd expect to happen if the hypothesis were true, so it's clearly not the weakener we seek.
No doubt you noticed the element of causation here—the study centers around a fairly textbook case of cause-and-effect. As you'll see, the logical elements presented thus far rarely occur in isolation. So let's take stock of where we are, and then move on to questions that combine the various features highlighted in the previous questions.
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