Professor: A marine biologist argues that transmission of sea lice

The marine biologist's conclusion is that "transmission of sea lice from farm salmon to wild salmon is unlikely in the Broughton Archipelago, British Columbia." His/her evidence for this conclusion is that:

• Numerous studies suggest that salinities less than 30 parts per thousand are unfavorable to sea-lice survival.
• The archipelago has a salinity range of 25–30 parts per thousand between March and June, the critical period for wild salmon migration
• These conditions tend to suppress sea-lice proliferation

Notice that even though the word "concludes" is used later in the passage, the marine biologist's ACTUAL conclusion is stated in the first sentence. All of the subsequent information is there to SUPPORT the claim that "transmission of sea lice from farm salmon to wild salmon is unlikely in the Broughton Archipelago, British Columbia." In this context, "concludes" just links one supporting premise to another.

Then, the professor (not the marine biologist) states: "But a review of the literature shows that salinities of 25–30 parts per thousand in combination with British Columbia's cool spring temperatures favor the flourishing of sea lice."

This statement attacks a premise of the biologist's argument: that the conditions in the Broughton Archipelago "tend to suppress sea-lice proliferation."

So, how exactly does the professor undermine the biologist's argument?

The biologist never discusses a condition that is necessary for sea-lice survival -- he/she only talks about a condition (low salinity) that is unfavorable to sea-life survival.

Even if you squint your eyes really hard and say that the biologist's argument implies that somewhat higher salinity is necessary for survival, that would not be totally accurate. At most, we can infer that higher salinity is more favorable to sea-lice survival, which is different than the condition being absolutely necessary. Because the biologist never claims that anything is absolutely necessary to sea-lice survival, it is not accurate to say that the professor undermines such a claim.

Eliminate (A).

The professor doesn't think that the salinity measurements were inaccurate -- in fact, he/she uses the same numbers in his/her own argument. Eliminate (B).

The biologist thinks that sea lice transmission is unlikely because the conditions in the archipelago "tend to suppress" sea-lice proliferation. The professor provides additional information, and then says that, actually, the conditions "favor the flourishing of sea lice."

Because the information provided by the professor completely contradicts the biologist's premise, we can determine that this additional evidence shows that the biologist's premise is false.

(C) is looking good.

The professor never questions WHERE the biologist got his/her information, or the validity of those sources. (D) is out.

Nope, the professor doesn't attack the connection between the biologist's conclusion and premises. Instead, he/she provides additional evidence to attack a premise, which in turn calls the biologist's conclusion into question.

(E) is out and (C) is the correct answer.

I hope that helps!