Answer:
B. Asking a yes-no question.
Step-by-step explanation:
If you ask someone to answer yes or no to a particular question, then the discussion ends there - there isn't much to elaborate on with such closed questions. However, if you talk about something your classmate is interested in, if you make sure they know you listened to them talking earlier, or if you ask them an open-ended question where they can express their feelings and opinions, they will be more likely to participate in the discussion.
If you create a pleasant atmosphere where everyone can feel welcome to speak themselves, then it will be a successful discussion.