When和While的区别 ①when是at or during the time that,既指时间点,也可指一段时间,while是during the time that,只指一段时间,因此when引导的时间状语从句中的动词可以是终止性动词,也可以是延续性动词,而while从句中的动词必须是延续性动词.②when 说明从句的动作和主句的动作可以是同时,也可以是先后发生；while 则强调主句的动作在从句动作的发生的过程中或主从句两个动作同时发生.③由when引导的时间状语从句,主句用过去进行时,从句应用一般过去时；如果从句和主句的动作同时发生,两句都用过去进行时的时候,多用while引导,如：a.When the teacher came in,we were talking.当此句改变主从句的位置时,则为：While we were talking,the teacher came in.b.They were singing while we were dancing.④when和while 还可作并列连词.when表示“在那时”；while表示“而,却”,表对照关系.如：a.The children were running to move the bag of rice when they heard the sound of a motor bike.孩子们正要跑过去搬开那袋米,这时他们听到了摩托车的声音.b.He is strong while his brother is weak.他长得很结实,而他弟弟却很瘦弱.
一般过去时：概念：过去某个时间里发生的动作或状态；过去习惯性、经常性的动作、行为.标志词：ago,yesterday,the day before yesterday,last week(year,night,month…) just now,基本结构：①be动词；②行为动词 否定形式：①was/were+not;②在行为动词前加didn't,同时还原行为动词.一般疑问句：①was或were放于句首；②用助动词do的过去式did 提问,同时还原行为动词.理解（概念）：什么是过去进行时?(1) 表示过去某时正在进行的状态或动作.例如：They were singing songs from seven to nine last night.昨天晚上七点到九点的时候他们一直在唱歌.(2) 由when 引导的时间状语从句,表示过去某一时刻,当一个动作发生时,另一个动作正在进行；或某一动作正进行时,突然发生另外一件事.It was raining when they arrived at the station.他们到达车站的时候,天正在下雨.(3) 由while 引导的时间状语从句,常表示在过去某一时刻发生的事情是可延续的或同时发生的,此时,主从句的动词都可用过去进行时.例如：He was selling the newspaper while he was waiting for the bus.他边等车边卖报.