Read the following conversation and answer the question.

M: Maths Department, Dr Webster speaking.

W: Hello, Professor 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's lost his voice and can't talk to you himself.

M: Lost his voice? That's too bad. Is there anything I can do for him?

W: Well, he has a class this afternoon from 2:30 to 4:00, and he won't be able to make it.

M: Does he want me to try to find somebody else to teach it?

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 exam papers. He's already marked them. And they're on the desk in his office. The whole thing wouldn't take more than...Oh, ten minutes or so.

M: 2:30, you say? Well, I'm free then, and I am going there anyway, so I could do it for him. Where's his class?

W: Carter Hall, Room 214. Will you need his office key to get the exams? I could bring it to you.

M: Well, 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, Professor Webster.

M: My pleasure.

Question: What's Don's problem? 

- He can't find his office key.

- He's unable to talk.

- He doesn't like his classroom.


He's unable to talk.