When Mary came I on the piano.A. is playingB. playsC. was playingD. played

问题补充：

When Mary came, I on the piano.

A. is playing

B. plays

C. was playing

D. played

答案：

A. is playing

B. plays

(答案→)C. was playing

D. played

解析：考查时态：句意：当玛丽来的时候，我正在弹钢琴。从句意看，弹钢琴是过去某个时间正在发生，用过去进行时，选C。