The answer is C: Question the opponent's family background.
This is a form of a logical fallacy called, ad hominem, which is Latin for “to the person”. It addresses a faulty form of argumentation that, instead of focusing on the topic that the person who is making the argument is presenting, the focus is instead on attacking the person that is making the argument by addressing his or her character, motive, background or other information that is not related to the substance of the argument.