Lily thinks playing piano is exciting she often plays it in her free time.A. a B. the C.

问题补充：

Lily thinks playing piano is exciting, she often plays it in her free time.

A. a B. the C. /

答案：

解析：句意：Lily认为弹钢琴很令人高兴，她经常在业余时间弹。短语play the piano,弹钢琴；乐器前面通常加定冠词the，故选B。