第1个回答 2012-03-27
如果主句谓语动词表示的是短暂动作，从句时间状语指一段时间，则when，while，as都可用
as和when可与非延续性动词连用，而while只能与延续性动词连用
as和when都可用来指一段时间，但as强调主句和从句表示的动作同时发生，而while强调主句表示的动作是在while从句的动作延续中发生的
She sang as she went along她边走边唱歌
She sang while she went along她走路时一直在唱歌赞同
过去进行时表示过去某一时刻或者某段时间正在进行或发生的动作，常和表过去的时间状语连用，如： 1. I was doing my homework at this time yesterday. 昨天的这个时候我正在做作业。 2. They were waiting for you yesterday. 他们昨天一直在等你。 3. He was cooking in the kitchen at 12 o'clock yesterday. 昨天12点，他正在厨房烧饭。 过去进行时的构成： 肯定形式：主语+was/were+V-ing 否定形式：主语+was not (wasn't)/were not (weren't)+V-ing 疑问形式：Was/Were+主语+V-ing。 基本用法： 1. 过去进行时表示过去某一段时间或某一时刻正在进行的动作。常与之连用的时间状语有，at that time/moment, (at) this time yesterday (last night/Sunday/week…), at+点钟+yesterday (last night / Sunday…)，when sb. did sth.等时间状语从句，如： 1）What were you doing at 7p.m. yesterday? 昨天晚上七点你在干什么？ 2）I first met Mary three years ago. She was working at a radio shop at the time. 我第一次遇到玛丽是在三年前，当时她在一家无线电商店工作。 3）I was cooking when she knocked at the door. 她敲门时我正在做饭。 2. when后通常用表示暂短性动词，while后通常用表示持续性动词，而while所引导的状语从句中，谓语动词常用进行时态，如： When the car exploded I was walking past it. = While I was walking past the car it exploded. 3. when用作并列连词时，主句常用进行时态，从句则用一般过去时，表示主句动作发生的过程中，另一个意想不到的动作发生了。如： I was walking in the street when someone called me. 我正在街上走时突然有人喊我。 4. when作并列连词，表示“（这时）突然”之意时，第一个并列分句用过去进行时，when引导的并列分句用一般过去时。如： 1）I was taking a walk when I met him. 我正在散步，突然遇见了他。 2）We were playing outside when it began to rain. 我们正在外边玩，这时下起雨来了。 过去进行时和一般过去时的用法比较： 1）过去进行时表示过去正在进行的动作，而一般过去时则表示一个完整的动作。 例如：They were writing letters to their friends last night. 昨晚他们在写信给他们的朋友。（没有说明信是否写完） They wrote letters to their friends last night. 他们昨晚写了信给他们的朋友。（表达了他们已写好的意思，整个写的过程已完成。） 2）当动作延续较长时间时或表示厌烦、赞美等感情色彩时，常用过去进行时表示。 例如：He was thinking more of others than of himself. 他考虑别人的比考虑自己的多。（表示说话者赞扬的口气） The boy was always making trouble then. 那时，他总是惹麻烦。（表示说话者厌烦的口气） 3. 状语从句: 在复合句中，修饰主句的动词,形容词或副词等的从句叫做状语从句。状语从句根据它表达的意思可分为时间、原因、条件、比较、目的、结果和让步等类型。 (根据考试说明,前四个要求掌握,其它要求理解) 时间状语（常由下列从属连词引导） when, as ,while (当……时候； 一边…… 一边……；在……期间)， before(在……之前)， after (在……之后)， as soon as（一…… 就…… ) since (自从……时起到现在)， till/until (直到……时) 等 例如： 1）When my cousin came yesterday, I was playing volleyball. 昨天我表哥来的时候，我在打排球。 2）When the air moves, it is called wind. 空气流动，就产生风。 3）As the boys walked along the lake, they sang happily. 这些男孩一边沿湖边走，一边愉快地唱歌。 4）While I was sleeping, the UFO arrived. 当我在睡觉时，UFO到达了。 when和while引导时间状语从句的区别： when表示“当……的时候”。从句中既可用延续性动词，又可用非延续性动词，这些动词既可以表示动作，又可表示状态。从句中的动作既可和主句的动作同时发生，又可在主句的动作之前或之后发生。 例如：Mary was having dinner when I saw her. The boy was still sleeping when his mother got home yesterday morning. When the teacher came in, the students stopped talking. while表示“在……的时候”、“在……期间” 、“一边……一边……”。while从句中必须是表示动作或状态的延续性动词。它强调主句的动作与从句的动作同时发生或主句的动作发生在从句的动作过程中。 例如：The weather was fine while we were in Beijing. She called while I was out. I was drawing while my brother was reading. He likes reading a newspaper while he is waiting for the bus. 如果主句的动作在从句的动作过程中发生，从句常用进行时。 例如：While we were swimming, someone stole our clothes. Don't talk so loud while others are working. 有时when 和while 可以转换使用。 例如：The girl was watching TV when the alien got in.