Are you good at?A. swimB. swimmingC. to swimD. swam

问题补充：

Are you good at?

A. swim

B. swimming

C. to swim

D. swam

答案：

A. swim

(答案→)B. swimming

C. to swim

D. swam

解析：考查短语 be good at doing 擅长做某事，所以选B 。