前后的时态要看具体的问题. 一般表示过去某个时间正在进行的动作,如: what were you doing when he came in. doing是一个持续性的动作,所以用过去进行时,而came是短暂性的动作,用一般过去时.when 长用于表示短暂性的动作.而while则多是说明持续性的动作.what wreyou doing while he wasdoing his homework.
when和 while 都可以引导时间状语从句, 表示一个动作发生另一个动作正在进行,如: when his mother came home, he was doing his homework. while he was waiting for the bus he read a book. when he was sleeping his father cam eback. 前后的时态要按实际情况来确定。
第2个回答 2006-04-23
i was doing my homework when my mother came home yesterday.
i was doing my homework while my father was busy working in his office last night.