The answer is A: Asking rhetorical questions.
When engaged in a discussion, formal or otherwise, it is never helpful to ask rhetorical questions since these kinds of questions merely solicit a dramatic effect whose aim is not really to receive an answer but rather to make a point which, in turn, is a poor device to be used in a discussion since what is expected of a discussion is the engagement in dialogue to promote debate, consensus, or disagreement by means of founded arguments.
