Explanation

Premises

1) infection by the SV40 virus is a contributing cause of mesotheliomas, since in the United States 60 percent of tissue samples from mesotheliomas, but none from healthy tissue, contain SV40.
2) SV40 is a monkey virus
3) however, in 1960 some polio vaccine was contaminated with the virus- SV40


Researcher’s conclusion/hypothesis-

The contaminated polio vaccine was the source of the virus found in mesotheliomas decades later.

We need to find an option that strengthens the Researchers’ conclusion/hypothesis.

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

This neither strengthens nor weakens the researchers’ conclusion. It is irrelevant. Eliminate

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

The hypothesis is that the contaminated polio vaccine was the source of the virus found in mesotheliomas decades later. Whether the changes in the technique of manufacturing the vaccine now prevent contamination with SV40 or not does not strengthen the hypothesis. Eliminate

Option C- Recently discovered samples of the vaccine dating from 1960 still show traces of the virus.

Read the premises again.
3) however, in 1960 some polio vaccine was contaminated with the virus- SV40

We need to find an option that strengthens the hypothesis that the contaminated polio vaccine was the source of the virus found in mesotheliomas decades later. Option C only restates the premise. Eliminate

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

The researchers' hypothesis/conclusion is about mesothelioma and the contaminated polio vaccine, not exposure to asbestos. Eliminate

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

Hypothesis- The contaminated polio vaccine was the source of the virus found in mesotheliomas decades later.

Option E supports the hypothesis. In Finland, where the polio vaccine was not contaminated, samples from mesotheliomas do not contain SV40.. This supports the hypothesis that the contaminated polio vaccine was the source of the virus- SV40 found in mesotheliomas. Hence correct.