PT 62 S4 Q19

   Doctor:Medical researchers recently examined a largegroup ... ...

The reasoning in the doctor's argument is most vulnerable to the criticism that it fails to consider which one of the following possibilities?
(A) A factor that need not be present in order for a certain effect to arise may nonetheless be sufficient to produce that effect.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Complete Section: LR-B, Dec. '10 LSAT (PT 62 Sec. 4)