—Mike invited us to take part in the party this Sunday.—Is tomorrow his birthday? A. Why n

问题补充：

—Mike invited us to take part in the party this Sunday.

—Is tomorrow his birthday?

A. Why not?

B. That’s all right.

C. What for?

D. What a good idea!

答案：

A. Why not?

B. That’s all right.

(答案→)C. What for?

D. What a good idea!

解析：根据Is tomorrow his birthday?可知，对方应该是很惊讶，不知为什么会邀请我们去参加晚会，故应该用what for。所以本题选C。