Read the following conversation and answer the question.

W: It seems you've burned yourself out.

M: Pardon. I'm afraid I didn't quite catch you.

W: You look tired. You must have overworked yourself.

M: Yes, a little bit. I've been hitting the books all these days.

W: Why have you been studying so hard?

M: I need to review my English.

W: So that's what keeps you so busy recently!

M: Yes, I've been tied up with my studies. Now, what worries me a lot is my English.

W: But why? Your English is very good.

M: Thank you. You are very kind.

W: No, I'm telling the truth. As an American, I understand you quite well.

M: It's very kind of you to say so.

Question: What makes the man feel tired? 

- Working in the sun.

- Carrying the woman's books.

- Going over his English.


Going over his English.