How Does the Ad Hominem Fallacy Involve Credibility

Multiple Choice

How does the ad hominem fallacy involve credibility?

A) It assigns expert credibility to someone who doesn't deserve it.
B) It fails to recognize the credibility of someone who is an expert.
C) It assigns too much credibility to an opponent.
D) It attacks the credibility of an opponent.
E) It ignores the issue of whether or not an opponent has credibility.