GWD-10-Q9 求助...

momohe

GWD-10-Q9

Although exposure to asbestos is the primary cause of mesothelioma, a slow-developing cancer, researchers 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. Researchers 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?

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A.
SV40 is widely used as a research tool in cancer laboratories.

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 traced 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.

请问B为什么不正确？如果现在的vaccine不含SV40了，那么不就说明原来的vaccine was the source of the virus decades later么？如果现在的vaccine还含的话，没准就是现在的vaccine是source了？

season5924

The way I looked at the problem is the following:

1) Read the question stem: Which of the following, if true, most strongly supports the researchers' hypothesis? Okay, this is a strengthen-type question.

2) Read the stimulus and find the researcher's hypothesis : this (polo) vaccine was the source of the virus found in mesotheliomas decades later. In short, contamination of virus in polo vaccine --> virus found in mesotheliomas.

3) Study the answer choices to find the strengthener.
A.SV40 is widely used as a research tool in cancer laboratories.  Irrelevant.

B.Changes in the technique of manufacturing the vaccine now prevent contamination with SV40.  Who cares about what is happening NOW?

C.Recently discovered samples of the vaccine dating from 1960 still show traced of the virus. The stimulus already stated such fact.

Both (D) and (E) look interesting.  However the phrase "a small percentage" in answer (D) bothers me. Even if (D) is right, it could only support "a small percentage" of the argument.  

4) Let's see (E) -- In Finland, where the polio vaccine was never contaminated, samples from mesotheliomas do not contain SV40.
Hmmm. Very sexy.  One way to strengthen an argument is to show that when the cause does not occur, the effect does not occur. In our case, this would lead to the following equation:
NO contamination of virus in polo vaccine --> NO virus found in mesotheliomas.  That is exactly what is said in answer (E).  Bingo.

If you are puzzled by the fact that the Finland sample contains no virus, then you should read the stimulus again. SV40 virus is ONLY a contributing cause, not a sufficient one! As I said in step 2 above, the focus is on the source of the virus, not the cause of the disease.

Fadaways

我觉得E还是有个问题：如果vaccine中没有SV40，结果m的样本中也没有，岂不是也说明SV40也不是m的致病原因之一？
我就是觉得这个有weaken的意思，所以才选了C。

arthurman

A.
SV40 is widely used as a research tool in cancer laboratories.

无关选项。虽然我们可以推导SV40因为被广泛使用所以比较有可能泄漏或者污染vaccine。但是该选项没有任何这样的信息来支持这个推断。

B.
Changes in the technique of manufacturing the vaccine now prevent contamination with SV40.

这些change只影响以后的vaccine。题目问的是之前某个时间段发生的事情的原因。

C.
Recently discovered samples of the vaccine dating from 1960 still show traced of the virus.

因为科学家已经发现了1960年的vaccine有virus。这个发现只能再次证明vaccine被污染过，但无法证明vaccine是mesotheliomas的源头。举个简单的例子，可能这些vaccine压根就没被注射过。

D.
In a small percentage of cases of mesothelioma, there is no history of exposure to asbestos.

该选项只能证明asbestos不是导致mesothelioma的唯一原因。和科学家的假设无关。



E.
In Finland, where the polio vaccine was never contaminated, samples from mesotheliomas do not contain SV40.

这个选项提供了比较对口的信息来支撑假设vaccine was the source of the virus found in mesotheliomas，即contaminated vaccine和mesotheliomas的关系。

所以我选E。

crystalbain

E?