I am not really sure about the justification given for both the cases presented to justify against the conclusion that the premise is false. I do think that the premise can easily be true if cool temp is an additional evidence, considering which professor is make his argument but this surely does not convey that the premise as false because cool temp is basically giving an additional reason for professor's conclusion. We cannot say the biologist is wrong because we do not have an evidence to show his premise is false. If his premise is true, then also professor can make use of his premise + cool temp to argue that this would be favourable to transmission of sea lice.
Vordhosbn wrote:
GMATNinja what is the role of "in combination with British Columbia's cool spring temperature" here? It looks like an additional premise to me? It reads like "well, the professor didn't read this one paper that found 30 part and less salines in combination with cool temperature flourishes the lice". If my argument has an added premise (x+y) with x being the common overlap how would this structure be considered as attacking x? To me it sounded the biologist wasn't aware of this one edge case (i.e., cool weather). Could you please help understand what I'm missing here?
Let's start by considering the structure of the marine biologist's argument.
The marine biologist concludes that "the archipelago's 25–30 parts per thousand salinity range between March and June...tends to suppress sea-lice proliferation." This conclusion is based on the premise that the salinity in this area is 25-30 parts per thousand in the spring, and that "salinities less than 30 parts per thousand are unfavorable to sea-lice survival."
So the marine biologist's conclusion relies on the premise that "salinities less than 30 parts per thousand are unfavorable to sea-lice survival." The professor then undermines the argument by
attacking this premise. More specifically, the professor claims that "salinities of 25–30 parts per thousand in combination with British Columbia's cool spring temperatures favor the flourishing of sea lice."
As a result, the premise that "salinities less than 30 parts per thousand are unfavorable to sea-lice survival" is false, which makes (C) correct.
You raise an interesting question about cool spring temperatures being an "edge case" of an otherwise reliable premise. Should we assume the premise that "salinities less than 30 parts per thousand are unfavorable to sea-lice survival" is generally sound? If so, would that make it true?
Unfortunately, the passage doesn't give us any evidence to help resolve this question. We know that the marine biologist has cited numerous studies, but we have no idea how complete or representative those studies are. All we know is that the professor claims the premise is not ALWAYS true. In other words, the professor claims the premise is false.
Yet even if we could somehow prove that the professor's point about cool spring temperatures was just an "edge case," how would that affect the premise?
Notice the premise doesn't say that salinities less than 30 parts per thousand are GENERALLY unfavorable to sea-lice survival, but simply that they ARE unfavorable to sea-lice survival. So if
any situations arise where salinities less than 30 parts per thousand are
favorable to sea lice, that would show the premise as written is false. So either way, (C) is the best answer.
I hope that helps!