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A distemper virus has caused two-thirds of the seal population in the

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A distemper virus has caused two-thirds of the seal population in the [#permalink] New post   02 Oct 2017, 21:45
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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.

The argument concerning the immune system of the seals presupposes which one of the following?


(A) There has been a gradual decline in the seal population of the North Sea during the past two centuries.

(B) No further sources of pollution have been added since May 1988 to the already existing sources of pollution in the North Sea.

(C) There was no sudden mutation in the distemper virus which would have allowed the virus successfully to attack healthy North Sea seals by May 1988.

(D) Pollution in the North Sea is no greater than pollution in the Mediterranean Sea, off the coast of North America, or in the Sea of Japan.

(E) Some species that provide food for the seals have nearly become extinct as a result of the pollution.



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Re: A distemper virus has caused two-thirds of the seal population in the [#permalink] New post   01 Mar 2021, 09:45
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broall wrote:
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.

The argument concerning the immune system of the seals presupposes which one of the following?


(A) There has been a gradual decline in the seal population of the North Sea during the past two centuries.

(B) No further sources of pollution have been added since May 1988 to the already existing sources of pollution in the North Sea.

(C) There was no sudden mutation in the distemper virus which would have allowed the virus successfully to attack healthy North Sea seals by May 1988.

(D) Pollution in the North Sea is no greater than pollution in the Mediterranean Sea, off the coast of North America, or in the Sea of Japan.

(E) Some species that provide food for the seals have nearly become extinct as a result of the pollution.



Same passage with different stem question: LINK


Official Explanation



(A) No. This does not relate to the fact that the seal population has suffered a severe decline in population since 1988.

(B) No. Adding more sources of pollution would strengthen the argument.

(C) Yes. This is an all-things-being-equal argument. If all other factors are the same, then it must be the pollution that caused the seals to become more susceptible to the virus. So for the argument to be valid, it must assume that the virus has not increased in virulence.

(D) No. This has no affect on the argument. If we knew that the seal population also decreased dramatically in these areas, then it would support the argument. On the other hand, if we knew that the seal population did not change in these areas, then it would weaken the argument.

(E) No. Although one can theorize that lack of food caused the seals to become malnourished, in turn weakening their immune systems, the argument does not presume any particular mechanism by which the pollution affected the seals. There are many other scenarios (some more direct) which could explain how the pollution weakened the seals’ immune system.
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Re: A distemper virus has caused two-thirds of the seal population in the [#permalink] New post   02 Oct 2017, 23:13
broall wrote:
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.

The argument concerning the immune system of the seals presupposes which one of the following?

(A) There has been a gradual decline in the seal population of the North Sea during the past two centuries.

(B) No further sources of pollution have been added since May 1988 to the already existing sources of pollution in the North Sea.

(C) There was no sudden mutation in the distemper virus which would have allowed the virus successfully to attack healthy North Sea seals by May 1988.

(D) Pollution in the North Sea is no greater than pollution in the Mediterranean Sea, off the coast of North America, or in the Sea of Japan.

(E) Some species that provide food for the seals have nearly become extinct as a result of the pollution.

Source: LSAT

Same passage with different stem question: LINK


C is the answer ...
Argument says that the decline in seal population is due to weakening of immune system that allowed virus to attack the seal...Pollution is the main cause for weakening of immune system ..
Negate C , it will point alternate reason for the decline ..
There was sudden mutation in the distemper virus which would have allowed the virus successfully to attack healthy North Sea seals by May 1988.
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Re: A distemper virus has caused two-thirds of the seal population in the [#permalink] New post   09 Oct 2017, 23:25
broall wrote:
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.

The argument concerning the immune system of the seals presupposes which one of the following?

(A) There has been a gradual decline in the seal population of the North Sea during the past two centuries.

(B) No further sources of pollution have been added since May 1988 to the already existing sources of pollution in the North Sea.

(C) There was no sudden mutation in the distemper virus which would have allowed the virus successfully to attack healthy North Sea seals by May 1988.

(D) Pollution in the North Sea is no greater than pollution in the Mediterranean Sea, off the coast of North America, or in the Sea of Japan.

(E) Some species that provide food for the seals have nearly become extinct as a result of the pollution.

Source: LSAT

Same passage with different stem question: LINK




Negating option C tells us "the virus has mutated and attacked healthy seals" hence this makes the argument to fall.
answer C
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Re: A distemper virus has caused two-thirds of the seal population in the [#permalink]
09 Oct 2017, 23:25
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