Some batches of polio vaccine used around 1960 were contaminated with SV40, a virus that in monkeys causes various cancers. Some researchers now claim that this contamination caused some cases of a certain cancer in humans, mesothelioma. This claim is not undercut by the fact that a very careful survey made in the 1960s of people who had received the contaminated vaccine found no elevated incidence of any cancer, since . (A) most cases of mesothelioma are caused by exposure to asbestos
(B) in some countries, there was no contamination of the vaccine
(C) SV40 is widely used in laboratories to produce cancers in animals
(D) mesotheliomas take several decades to develop
(E) mesothelioma was somewhat less common in 1960 than it is now