A distemper virus has caused two-thirds of the seal population in the North Sea to die since May 1988. The explanation for the deaths cannot rest here, however. There must be a reason the normally latent virus could prevail so suddenly: clearly the severe pollution of the North Sea waters must have weakened the immune system of the seals so that they could no longer withstand the virus.

Which one of the following, if true, most strongly supports the explanation given in the argument?
(A) At various times during the last ten years, several species of shellfish and seabirds in the North Sea have experienced unprecedented steep drops in population.
(B) By reducing pollution at its source, Northern Europe and Scandinavia have been taking the lead in preventing pollution from reaching the waters of the North Sea.
(C) For many years, fish for human consumption have been taken from the waters of the North Sea.
(D) There are two species of seal found throughout the North Sea area, the common seal and the gray seal.
(E) The distemper caused by the virus was a disease that was new to the population of North Sea seals in May 1988, and so the seals’ immune systems were unprepared to counter it.
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E actually weaks the conclusion.

The argument states that was the pollution the reason that weakened the immune system, and therefore the seals could no longer withstand the virus.
As per E it was the virus itself what weakened the immune system.

The OA must support that was the pollution and no other thing the responsible of the immune system weakness.

Hope that helps.
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Yeah, it's weird.

A) Seems to imply that the North Sea is a sketchy place for things to live, not for just the seals
B) Implies that yes, there is pollution kicking around in the North Sea
C) Is completely irrelevant
D) Same with this one, we don't care
E) This is probably what I would have chosen too, simply because it seems the most related. It points out that back in the day, the virus' disease was a toughie for the seals' immune systems... but that's kind of par for the course for most new diseases in any animal population.

After some thought, I'll have to go with A. None of the answers seems to support a direct link between pollution and seal immune systems. But A and B both at least demonstrate that the pollution is even there. A goes further than B and implies that there's enough troubling conditions in the area to cause ecological damage.

IMO none of the answers provide good support at all... but the Q wants us to find the strongest, which in this case seems to be the best of a bad lot. For me if I saw that other animals were croaking in the same area as the seals that would at least provide a basis on which to take the pollution theory a bit more seriously!
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Yeah but it doesn't even imply that, so you can't make that assumption (it's unlikely that a virus that messes up seals in a specific way is going to cross to other species anyway). I can come up with all kinds of assumptions about all of the answers to both improve and dissolve their supportive capacity for the argument... but that of course is not the point. You can only take what is directly stated as truth and then see which truths, however absolutely distant, are the closest (relatively) to supporting the argument. And for me that remains A after the discussion here that helped me see where E falls short.

Seems the best thing you can do is post the OA. That way we can all work backwards and try to fetter out the reasoning!
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It's probably because none of the answers really make a solid connection between the pollution and the immune systems of the seals. So we're forced to pick the answer that comes the closest. When making my final decision, I looked at it as if I had been called to investigate whether or not the argument (pollution weakens immune system) was true or not. However my time is valuable (hypothetically ) so I want to know if I should even waste my time.

Treating each of the answers as a "reason" to go ahead and investigate, which is the most compelling?

Obviously not C or D because they're obviously not even close to being related to the topic.

B is a bit interesting because it implies that pollution does exist in the North Sea but I can readily assume that water pollution exists all over the place, so why do I care?

E is an interesting fact... but doesn't add anything that I don't already know or could have easily inferred.

But A notes that things are often dying in hordes out in the North Sea. While this does not say anything about seals or pollution or even viruses, it makes me raise an eyebrow and think "huh, maybe there is something funky going on out there. We should probably check it out." In more formal terms, A provides plausible evidence for a common variable in animal death in the North Sea. Based on general knowledge, this is more likely to do with some sort of shift in the ecosystem than it is to do with a seal virus.

It's tempting to start dreaming up reasons why A COULD be wrong: like you said... maybe it IS the virus that's killing birds. Maybe the death of the seals is messing up the food chain? But we don't know, so we have to keep an open mind about it. Maybe it is the pollution that's killing birds and sea life... so maybe it IS the pollution that's leading to seal death as well. None of the other answers really invoke that line of thinking as well as A does.
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dalmba has explained it above.
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Great question....I am still bit apprehensive about A.

A

(A) At various times during the last ten years, several species of shellfish and seabirds in the North Sea have experienced unprecedented steep drops in population --> In argument “There must be a reason the normally latent virus could prevail so suddenly” explains that there is something else in north sea causing deaths of shellfish (Pollution). This to some extent supports the argument
(B) By reducing pollution at its source, Northern Europe and Scandinavia have been taking the lead in preventing pollution from reaching the waters of the North Sea --> weaken
(C) For many years, fish for human consumption have been taken from the waters of the North Sea --> weaken by countering the argument with another reason
(D) There are two species of seal found throughout the North Sea area, the common seal and the gray seal --> out of scope
(E) The distemper caused by the virus was a disease that was new to the population of North Sea seals in May 1988, and so the seals’ immune systems were ..” --- >weaken

E?
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