听力原文：M: Math Department, Doctor Webster speaking. W: Hello, Prof. Webster, this is Janet Smith calling. I'm living two doom down from your teaching assistant, Jack Williams. Jack 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: 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 to 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 tan minutes. M: His classes are two-thirty, eh? Well, fortunately, I will be on campus at that time anyway so I could do it for him. What room is his class in? W: Lecture Hall Three, Room Two-fourteen. 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. W: Thank you very much, Prof. Webster. Jack doesn't have another class to teach until Thursday, and hopefully, he will be able to talk by then. He'll call you as soon as he can. Oh, yes, I almost forgot. Could you put the next assignment on the board, too? It's all the problems on page forty-five, and they are due at the next class. (23)