I my homework while my mother was reading a book last night.
A. did
B. do
C. was doing
D. were doing
网友回答
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。