while 的用法:
1)用在表示进行时态的句子中:
如:While he was doing homework,Jim came in.
2)用在两个动作同时进行的句中:
如:While he was dancing,Jim was singing.
3)表示对比,但没有发生转折:
如:While he is a student,she is a teacher.
4)表示状态:
如:While he was at home,he finished his homework.
总之,只要句中出现了Be动词,不管句子的意思如何,表示"当"这个意思的时候,正式场合都用"while".