如题所述
while "当……时候",有表示一段时间的含义在里面,引导时间状语从句,所以它后面的句子的谓语动词是连续性的或表状态的,其时态可以是一般时态(表状态)或进行时态(连续性动作):
He saw a snake while he was in the mountains.他在山里的时候见到了一条蛇。
I was doing my homework while my brother was playing with his toys. 我弟弟在玩玩具的时候我在做家庭作业。