PT 66 S2 Q5

Bacteria that benefit human beings when they arepresent in the body are ... ...

Which one of the following, if true, most seriously undermines the argument’s reasoning?
(A) Stomach ulcers caused by H. pylori and tuberculosis can both be effectively treated with antibiotics.
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in June 2012 LSAT (PT66): Logical Reasoning A