问题补充:
I my homework while my mother was reading a book last night.
A. did
B. do
C. was doing
D. were doing
答案:
A. did
B. do
(答案→)C. was doing
D. were doing
解析:句意:昨晚当我的母亲正在读书时,我正在做作业。While引导时间状语从句时,强调动作的同时发生,结合语境可知主句描述的是过去正在进行的动作,句子主语是I,故助动词用am的过去时态was,选C。