Answer: a. the people who do not support the new library building must be uneducated and stupid.
Explanation: "Ad hominem" means "against the man" and when used in a discussion, it means to attack a person, or a group of persons, to shoot down their argument instead of using a logic argument. In the given sentences the one that uses "Ad hominem" is option a, because it attacks the people who do not support the new library building, by saying they are "uneducated and stupid" instead of giving a logical argument to why the new library should be built.
