while 的用法:
1)用在表示進行時態(tài)的句子中:
如:While he was doing homework,Jim came in.
2)用在兩個動作同時進行的句中:
如:While he was dancing,Jim was singing.
3)表示對比,但沒有發(fā)生轉(zhuǎn)折:
如:While he is a student,she is a teacher.
4)表示狀態(tài):
如:While he was at home,he finished his homework.
總之,只要句中出現(xiàn)了Be動詞,不管句子的意思如何,表示"當(dāng)"這個意思的時候,正式場合都用"while".