TOEFL Listening: ETS-TOEFL听力机经 - D16AN9WANJ3Z_5BKP$

Why does the professor say this: A. He hopes that one of the students will explain the answer to the others. B. He believes that the answer should be obvious to the students. C. He thinks the point is not relevant to today's lecture. D. He does not remember if he covered the point in another lecture.