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#11 - Human skin gives off an array of gaseous substances

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Please post below with any questions!
lang023
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Hello,

I have a question on this problem. I chose E, because for me it sounded like it could wreck the argument. Human skin always gives off gaseous substances that repel mosquitoes. The question stem says that gaseous substances attract mosquitoes, so how is this answer choice wrong? Thank you!
Alex Bodaken
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lang023,

Thanks for the question! Let me see if I can help.

I believe in your comment you are referencing the Assumption Negation Technique, which is absolutely a tool you can and should be using with Assumption problems like this one. Let's use that with both answer choice (E) and the credited answer choice (B) and see if we can't figure out what this issue is.

Answer choice (E) reads: Human skin never gives off any gaseous substances that repel mosquitoes. You note in your comment that the negation would be Human skin always gives off gaseous substances that repel mosquitoes. Careful here! Recall that we are looking for the logical opposite of the answer choice - and the logical opposite of "never" is "sometimes" (not "always"). If you are a PowerScore student, make sure you review those logical opposites in the Bible or the Coursebooks...it doesn't end up mattering here, but just a note :-D Anyway, the negation of answer choice (E) ends up being Human skin sometimes gives off gaseous substances that repel mosquitoes. Okay, so if this were true, would it weaken the author's conclusion that some other gaseous substance given off by human skin also attracts mosquitoes? Not particularly...in fact, if human skin sometimes gives off gaseous substances that repel mosquitoes, it may even slightly strengthen the idea that human skin is giving off other gaseous substance(s) that attracts mosquitoes, since (in this scenario) the mosquitoes are still choosing to bite the human arm, perhaps leading to the conclusion that the substances attracting the mosquitoes are overcoming whatever negative ones that repel the mosquitoes.

Answer choice (B) reads: Mosquitoes are not attracted to humans by body heat. This one is fairly easy to take the logical opposite of, it would read Mosquitoes areattracted to humans by body heat. If this were true, then, would it weaken the argument? It would: if mosquitoes are attracted by the body heat of humans, it weakens the idea that there must be a gaseous substance that is attracting them (it could just be the heat). Therefore, answer choice (B) is credited.

Hope that helps!
Alex
lang023
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Thank you, Alex for your detailed response!! Ugh, I think I was reading too much into the answer choices and made a silly error. Thank you again!
erust2
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Is D wrong because the stimulus says “even in darkness”? Therefore it doesn’t matter if it’s dark’or light?
Malila Robinson
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Hi erust2,
Yes! Your reasoning for D is correct. The level of success in darkness vs. light isn't a necessary aspect of the argument, so negating D doesn't hurt the argument.
Hope that helps!
-Malila
Margo
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Hi Powerscore,
I got this question correct (B) but I had trouble choosing between B and A.

(A) says that mosquitoes do not communicate with each other. If I apply the assumption negation technique it is: "mosquitoes sometimes communicate with each other." This seems to hurt the argument: If mosquitoes could communicate with each other, couldn't they communicate to find human arms even in the dark without visual cues? I would think that mosquitoes would communicate with each other more when they found a human arm than when they found the two gaseous substances.

Any help would be great :) I feel like I'm missing something here.
Adam Tyson
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It looks to me like you are working too hard to help answer A out here, Margo. Even if mosquitoes communicate with each other, in order for that information to hurt this argument and conclude that there may not be other gaseous substances, you would have to assume that 1) at least one mosquito saw the arm before it got dark, 2) that mosquito was able to let other mosquitoes know about the arm and how to find it even after it got dark, and 3) the arm didn't move after the first mosquito found it. Or, perhaps, you would have to assume that 1) a mosquito found the arm in the dark, without visual cues or the use of additional gaseous substances, maybe by just bumping into it by luck, and then 2) called out through the darkness to other mosquitoes to bring them to the location.

And still, even with all these extra added assumptions, none of that really helps explain why a bare arm in the darkness attracts more mosquitoes than either of those substances do in the absence of the arm. The author is giving evidence that those substances alone are not enough, so there has to be something more to the bare arm than just those gasses. He concludes that the extra something must be another gaseous substance. In making that claim, he has to assume that the mosquitoes are not attracted to something else about the arm, other than gaseous substances! Something like heat, perhaps?

Put more simply, this is a causal argument. Carbon dioxide and lactic acid cannot be the sole cause, because the bare arm attracts more than those substances to. The author concludes that the additional causal factor is another gas. The assumption is that it couldn't be something other than a gas, because if it was something other than a gas then the argument would fall apart.

Try not to help the answers! Take them on their own, as is, and see if they do what you need them to do. If they don't, then they are losers.

Good luck!
Adam M. Tyson
PowerScore LSAT, GRE, ACT and SAT Instructor
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