While Helen the piano her mother came inA. was playingB. is playingC. playedD. plays

问题补充：

While Helen the piano，her mother came in．

A. was playing

B. is playing

C. played

D. plays

答案：

(答案→)A. was playing

B. is playing

C. played

D. plays

解析：句意：当海伦正在弹钢琴时，她的母亲进来了。While引导时间状语从句，强调主从动作的同时发生，从句中常用进行时态，联系下文可知从句描述的是过去正在进行的动作，故用过去进行时态，选A。