听力原文：W: Hi, Rob, you know that class you missed yesterday？
M: Yes, but I was seriously iii.
W: I'm sorry to hear that. You (:an have my notes.
M: Thanks. I appreciate that.
W: So how are you feeling？
M: Much better now that I began taking an antibiotic. Doctor Lee gave me one, and it really helps. You know what amazes me is that how the human beings managed to survive before antibiotics.
W: I agree. When my father was a young boy in the 1940's, he got blood poisoning and would have died. But his doctor had heard of this new drug called penicillin.
M: Wow, he was really lucky. And now we have lots of antibiotics that kill bacteria.
W: Well, penicillin kills bacteria, but not all antibiotics do. Some are just slowing the bacteria down until our normal immune defenses can finish the job.
M: Wow! How do you know all these？
W: My mother used to look up all our medicines. There are lots of books around. It's interesting. What antibiotics are you taking？
M: I don't remember. It's on the bottle. I think I'll take a new look at the label and drop by the library to see if they have reference books on medicines. See you in the lab tomorrow.
(23)

A. The man's illness.
B. The effect of antibiotics.
C. The hobby of the woman's mother.
D. Their class.