－You quit the job? Are you crazy?－I’m serious.A. I don’t know for sure.B. I am behind you.

问题补充：

－You quit the job? Are you crazy?

－I’m serious.

A. I don’t know for sure.

B. I am behind you.

C. I’m not going to kid you.

D. Congratulations.

答案：

A. I don’t know for sure.

B. I am behind you.

(答案→)C. I’m not going to kid you.

D. Congratulations.

解析：考察交际用语。A我不确定；B我支持你；C我不是和你开玩笑的；D祝贺你。句意：—你放弃了你的工作？你疯了吗？—我不是开玩笑的，我是认真的。根据句意说明C正确。