tarek99 wrote:
Although exposure to asbestos is the primary cause of mesothelioma, a slow-developing cancer, researches believe that infection by the SV40 virus is a contributing cause, since in the United States 60 percent of tissue samples from mesotheliomas, but none from healthy tissue, contain SV40. SV40 is a monkey virus; however, in 1960 some polio vaccine was contaminated with the virus. Reseaches hypothesize that this vaccine was the source of the virus found in mesotheliomas decades later.
Which of the following, if true, most strongly supports the researchers' hypothesis?
(A) SV40 is widely used as a research tool in cancer laboratores.
(B) Changes in the technique of manufacturing the vaccine now prevent contamination with SV40.
(C) Recently discovered samples of the vaccine dating from 1960 still show traces of the virus.
(D) In a small percentage of cases of mesothelioma, there is no history of exposure to asbestos.
(E) In Finland, where the polio vaccine was never contaminated, samples from mesotheliomas do not contain SV40.
fameatop wrote:
I am not able to understand why option C is incorrect & E is correct. Can you kindly throw some light on the same. Waiting eagerly for your detailed explanation. Regards, Fame
Fame,
So, the argument presents, as evidence, the fact that "
in 1960 some polio vaccine was contaminated with the virus." That's evidence, so for GMAT purposes, that's fact beyond dispute. Then it makes the argument, the hypothesis, that SV40 in the vaccine CAUSED the SV40 in the mesotheliomas. That's the actual argument we are trying to support, the link between the SV40 in the vaccine and the SV40 in the mesothelioma tissue.
Well,
(C) merely strengthens the evidence. We already were told that there was SV40 virus in the polio vaccine. That's already beyond doubt. Statement
(C) strengthens this statement that is already beyond doubt, but it doesn't say squat about the link to mesothelioma. The researchers were hypothesizing this link between SV40 virus in the vaccines and mesothelioma, and
(C), while it verifies --- "
yep, there sure was SV40 in that polio vaccine!" --- doesn't bring us any closer to a link with with mesothelioma. The argument is all about that link.
By contrast,
(E) is very powerful. If the SV40 virus in the vaccines really is the source of the virus in the mesothelioma tissue, then if we found some case in which there was
no SV40 virus in the vaccine, then we would expect to find
no SV40 virus in the mesothelioma tissue.
(E) provides this new and very cogent evidence. This is new, different from what was stated in the passage, although it provides strong support to the passage. In general, if I make the argument that P and only P causes Q, then part of what I am predicting is --- if there's no P, then there should be no Q. That would be very powerful evidence for this claim, and this is precisely the nature of the powerful evidence that
(E) provides. That's why it's the best answer.
Does this make sense?
Mike