Questions where statement A and statement B contradict each other thus leading to an answer have been excluded from gmat as far as i know.
Imagine choice A being that X is not negative
Choice B being that X is not positive.
The question asking for a value of X.
Can yu say that X is 0.
IF the inference was derived from another fact then a valid question but in this type NO. Be very careful that these questions r *generally* NOT going to be a past of the gmat.