***while和when的用法***

这两个词都是引导时间状语从句:When引导的时间状语从句:表主句的动作和从句的动作同时发生,或从句的动作发生在主句之前。如：1。I was reading a novel when she came in。她进来的时候,我正读一本小说。（动作同时发生）2。When it rains,I go to school by bus。下雨的时候,我坐公花汽车上学样。（动作同时发生,都用现在时。）3。When he receives the letter,he'll tell us know。(动作相继发生,主句的动作发生在从句之前,动词用过去完成时,从句用过去式。）While引导的从句：表示“当。强调某一段时间内主句和从句中谓语动词所表示的动作同一时期发生。如:1。Never get on or off a bus while it is moving。汽车在运行时,不要上下车。(动作同时发生,动词都用现在时。)2。She listened closely while he read。他读时,她仔细听着。(动作同时发生,动词都用过去时。)3。While you are young,you must work hard。趁你年轻时,要努力工作。(主句的动作发生在从句运作发生的过程中。)4。I was doing my homework while my brother was playing。我做功课,而我弟弟在玩游戏。(while含有对比的意思)