PrepTest 146, Section 2, Question 11
Human skin gives off an array of gaseous(60 more words not shown)
The reasoning in the argument(7 more words not shown)
- AMosquitoes do not(4 more words not shown)
- BMosquitoes are not(6 more words not shown)
- CHuman skin gives(13 more words not shown)
- DMosquitoes are no(13 more words not shown)
- EHuman skin never(8 more words not shown)
Reading the argument
What if the mosquitoes are drawn to the arm's warmth?
The two gases attract them, but the real arm attracts them more. Something about the arm therefore seems to matter beyond the attraction supplied by those gases. The author concludes that it must be another gas. Why couldn't it be something else the arm provides?
What we’re looking for
Darkness removes visual clues, so we can't explain the difference by saying mosquitoes see the arm. But it doesn't remove body heat. For the required assumption, I'd look for a way to rule out that competing explanation. Otherwise, the extra attraction doesn't establish the extra gas.
Working the answers
- A
Mosquitoes could communicate with one another while some additional gas also attracts them. Nothing in the argument requires a complete absence of communication. Also, 'alone or combined' describes the two substances being tested, not mosquitoes being tested individually. We should not invent a single-mosquito experiment to eliminate this answer.
- BCorrect
The argument needs to exclude body heat as the reason a real arm attracts more mosquitoes than the two gases do. If warmth attracts mosquitoes, the arm's advantage could come from that warmth, without establishing any additional attractive gas. B removes the alternative we identified. It doesn't by itself prove that the additional gas exists; it blocks a gap in the stated reasoning.
- C
This compares daytime and nighttime amounts of gas. The passage instead compares an arm with two particular gases and removes vision as an explanation by testing in darkness. Darkness needn't even mean nighttime. We don't need a claim that skin releases more gas at one time of day.
- D
Visual cues could make an arm easier to find in light, and the argument could still concern what attracts mosquitoes in darkness. The author doesn't need mosquitoes to perform equally well under both lighting conditions. The point is that the two known gases don't fully account for the arm's attraction even without visual cues.
- E
A skin gas that repels mosquitoes could coexist with other gases that attract them. The combined effect could still be attraction. The argument doesn't need every gas released by human skin to work in the same direction; it needs a basis for identifying another attractive one.
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