PrepTest 105, Section 4, Question 5
The most reliable way to detect the presence(42 more words not shown)
Which one of the following(8 more words not shown)
- AThere are other(10 more words not shown)
- BNot all living(8 more words not shown)
- CWe are incapable(12 more words not shown)
- DSome living beings(8 more words not shown)
- EEarth is the(9 more words not shown)
Reading the argument
Methane might be useful evidence of life. But is it the most reliable test?
My first questions go in two directions. Could methane come from something other than life? And could there be life that doesn't produce methane? The next sentence addresses the first concern: the passage says methane disappears unless living beings keep replenishing it. Accepting that premise gives us a reason to connect a continuing supply of methane with life.
It still doesn't establish “most reliable.” We'd need to compare this test with the alternatives. There could be a better way to find life even if methane is a useful clue.
What we’re looking for
Since we're asked to weaken the argument, my main prediction is evidence of a more reliable method. A fact exposing a limitation of the methane test could also matter, but I would initially look for that better alternative.
Working the answers
- A
Other methods aren't necessarily better methods. There could be several alternatives, all less reliable than checking for methane. This resembles the prediction, but it omits the comparison we need to challenge “most reliable.”
- BCorrect
This returns to the other concern we raised: life without methane. If some living beings don't produce it, a planet could have life without those organisms replenishing methane in its atmosphere. A methane test could miss that life.
The given rule tells us why methane needs living beings to keep supplying it. It doesn't tell us that every kind of living being supplies methane. B exposes that limitation. It doesn't identify the better method I initially predicted, but it directly challenges the case for treating this test as the most reliable way to detect life.
- C
Being unable to perform a test now is different from the test being unreliable if performed. An instrument we haven't yet developed could provide highly reliable results. C challenges our present ability to use the proposed method, while the conclusion concerns how reliably determining methane's presence would detect life.
- D
A small amount is still methane. We aren't told that the amount would be too small to detect or that the organisms couldn't replenish it sufficiently. D doesn't establish the missing-methane problem B creates; we'd need another fact connecting small production to failure of the test.
- E
This tells us where methane has been detected so far, not how well the method would distinguish planets with life from those without it. Perhaps other atmospheres haven't been adequately examined. We don't get a case in which the test would miss life or a comparison showing another test is more reliable.
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