A、  B、  C、  A题目为附加了疑问词“aren’t you”的反意疑问句，这种情况F只需对前面的叙述部分作出回答就可以了。问的是下午是否有空，(A)给出了肯定的回答，因此为正确答案；(B)虽然也是用yes回答，但与问题

Can I leave a message for him?
(A) He should be back by Saturday.
(B) Certainly, I’ll pass it on.
(C) He had to leave in a hurry.

You are going to be free in the afternoon, aren’t you?
(A) Yes, do you need any help?
(B) Yes, I’m going to Tokyo tomorrow.
(C) It costs 20 dollars.