Assumption-CE. The correct answer choice is (C)
The stimulus for questions 37 & 38 contains causal argument. The passage tells us that two thirds of the seals in the North Sea seal have died from the normally latent distemper virus since May 1988. The author argues that North Sea pollution must have weakened the seals’ immune systems, and this in turn left them unable to withstand the virus:
- North Sea Pollution Weakened immunity 2/3 of seals succumb to distemper
Answer choice (A): This answer is not an assumption required by the argument, which deals with the North Sea seals since May 1988, not with two centuries of North Sea seal population trends. If we negate this answer choice (“there hasn’t been a gradual decline”), it has no effect on the strength of the argument in the stimulus.
Answer choice (B): This is not an assumption required by the argument in the stimulus, and if we apply the assumption negation technique, we get “further sources of pollution have been added…” This would do nothing to weaken the strength of the conclusion that the pollution must have weakened the immune systems of the North Sea seals.
Answer choice (C): This is the correct answer choice. This is an assumption is required of this argument, as it rules out an alternative explanation for the sudden prevalence of the distemper virus. If we negate this answer choice, we get “there was (some) sudden mutation in the virus that allowed it to successfully attack.” This would crush the conclusion in the stimulus.
Answer choice (D): This answer offers us irrelevant information about several bodies of water that are at least as polluted as the North Sea. This is certainly not an assumption required by the argument.
Answer choice (E): This answer in fact weakens the argument in the stimulus, offering an alternative cause for the seals’ weakened immunity—diminishing food supplies. This answer prchoice places the blame indirectly on the pollution, unlike the conclusion in the stimulus, that the pollution led directly to weakened immunity for the seals.