The most accurate sentence that defines the functions of bullet points is B "they break up the points and prevent the readers from getting overwhelmed".
That is so because the bullet points refer to key words or key ideas, which are meant to help the speaker to remember the sequence of ideas related to the topic he's talking about. They don't refer to complete sentences or else there would be no point in the speaker using them as the reader would read by himself. The bullet points allow the "surprise factor" which is very important in every presentation, catching the audienc's attention and interest in the topic.