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?
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 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.

For discussion. OA to follow