Which one of the following, if true, would most undermine the claim that ... ...

Which one of the following, if true, would most undermine the claim that prions cause CJD?
(A) Several symptoms closely resembling those of CJD have been experienced by patients known to have a specific viral infection.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in PT70 (Oct 2013): Reading Comprehension