问题补充：
--- What were your parents doing at eight last night?
--- My father was cooking while my mother .
A. watched TV
B. were watching TV
C. is watching TV
D. was watching TV
答案：
A. watched TV
B. were watching TV
C. is watching TV
(答案→)D. was watching TV
解析：句意：昨晚八点你的父母正在做什么？——我父亲一边做饭，我母亲一边看电视。结合语境可知下文描述的是过去某时正在进行的动作，while引导时间状语从句强调主从动作的同时发生，my mother为单数第三人称，故助动词用was，选D。
