A、Yesterday before dinner. B、Two days ago. C、Last weekend. D、One week ago. D

W: Hey! (13) Are you going to play some tennis this afternoon?
M: Well, to tell you the truth, (13) I’m not feeling so hot today.
W: Come on. How long has it been since we played?
M: A couple of days.
W: A couple of days? Come on. It’s been more than a couple of days.
M: Yeah. I guess you’re right. It’s been almost a week.
W: (14) It’s been exactly a week.（女士说他们有一个星期没打网球了。也就是说他们上次打网球是一周以前。）And we used to play at least three times a week.
M: I know. Playing right after class was something to look forward to.
W: Yeah. And it was right before dinner. So we build up our appetite.
M: (13) I’ve just been very busy, I guess. And my stomach is bothering me today.（女士邀请男士去打网球，但是男士说他今天没有那个热情，随后解释了原因： 他很忙而且还胃疼。后面详细解释了原因。可见对话是围绕男士为什么不想去打网球而展开的。）
W: But you look OK to me.
M: Well, I was up late with Steve in the library working on a project. We have to turn it in by tomorrow for that anthropology class. We’ve been working on it all weekend. And I was drinking a lot of coffee. I guess I just drank too much.
W: Listen. I took that class last semester. (15) And I could meet you in the library later tonight and help you if you want.（ 男士说他要完成人类学课的方案，女士说她可以帮助男士。）And then you have time to play tennis this afternoon.
M: Yeah. I guess my stomach doesn’t hurt that bad. And I could certainly use your help. But it’s also...
W: Is there something else bothering you?
M: Well, to be honest, I’m getting tired of losing.
Questions 13 to 15 are based on the conversation you have just heard.
13. What are the students mainly discussing?
14. When was the last time the speakers played tennis?
15. What does the woman offer to do for the man?