听力原文：M: Hi, Susan. Where were you at lunch time？ I was saving a seat for you in the ca

W: Oh, sorry to miss you. But my thirst for knowledge was greater than my hunger for food.

M: Ha. I never had that problem. So where were you？

W: My physics class ran overtime.

M: That's been happening quite a bit lately, hasn't it？

W: I guess so. Actually what happens is that a bunch of us hang around for a while after class to talk with our professor and ask him questions.

M: Oh, the professor is m popular. Who is he？

W: Professor Hall. Have you heard of him？

M: Hm, he does have a good reputation in the physics department.

W: And a well deserved one. The same students who fall asleep in the discussion group in seminars fight for front row seats in his lecture.

M: Oh, no. I hope he isn't catching.

W: You can joke. But it's great to have a professor who is not only interesting, but is prepared to give up time for students.

M: I know. There I really agree. Maybe I should sit in on his class some time. Do you think he would care？

W: Not at all! Lots of students bring their friends and he says he feels flattered.

(23)

A．Giving a lecture.

B．Discussing physics problems.

C．Waiting for a friend.

D．Reading twentieth-century literature.