They enjoy piano in their free time.A. playB. playingC. playing theD. to play a

问题补充：

They enjoy piano in their free time.

A. play

B. playing

C. playing the

D. to play a

答案：

A. play

B. playing

(答案→)C. playing the

D. to play a

解析：enjoy后面一般接名词或者动名词作宾语，动名词表示抽象动作，play后面接乐器时，要加定冠词the，故选C。