听力原文：M: Maths Department, Doctor Webster speaking.
W: Hello, Prof. Webster, this is Janet Hill calling. I live two doors down from your teaching assistant, Don Williams. Don asked me to call you because he has lost his voice and can' t talk to you himself.
M: Lost his voice. Oh, what a shame! Is there anything I can do for him？
W: Well, he has a class this afternoon from two-thirty to four and he won' t be able to teach it, but he doesn't want to cancel it either.
M: Does he want me to try to find somebody else to teach the Class？
W: No, not exactly. What he wants to do is to get someone go in for him, just to pass back the mid-term exams. He' s already marked them and they are on the desk in his office. The whole thing wouldn't take more than ten minutes.
M: His classes are two-thirty, you say？ Well, I' m free at that time, and I was going to be on campus anyway, so I could do it for him. What room is his class？
W: Cater Hall. Room 214. Will you need his office key to get the exams？ He' s given it to me and I could bring it to you.
M: Actually, that won' t be necessary. We have a master key in the maths department. So I can get into his office if necessary.
W: Thank you very much, Prof. Webster. Don doesn't have another class to teach until Tuesday, and hopefully, he will be able to talk by then. He' II call you as soon as he can. Oh, yes, I almost forgot.
M: Yes？
W: Could you put the next assignment on the board, too. It' s all the problems on page fourty-five, and they are due at the next class.
M: No trouble at all. Thanks for passing all the news about Don, and please tell him not to worry about anything.
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A. He can' t find his office key.
B. He has misplaced some exams.
C. He is unable to talk.
D. He doesn't like his classroom.