PT 37 S4 Q2

The vomeronasal organ (VNO) is found inside the noses of various animals. ... ...

Which one of the following, if true, most weakens the argument?
(A) It is not known whether the researchers succeeded in stimulating only VNO cells in the human subjects' noses.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in Practice Set: "Weaker" Questions, Set 1