He was impolite to the Custom Officer of course made things even worse.A. whoB. thatC

问题补充：

He was impolite to the Custom Officer, , of course, made things even worse.

A. who

B. that

C. what

D. which

答案：

A. who

B. that

C. what

D. which

解析：which引导非限制性定语从句,指代主句的整个情况。