专题：状语从句状语从句在句中作状语，修饰主句中的动词、形容词或副词等。状语从句放在主句之前时，常用逗号分开；放在主句之后，一般不用逗号。状语从句根据其句中表达的不同功能，可分为时间状语从句、地点状语从句、原因状语从句、目的状语从句、结果状语从句、条件状语从句、方式状语从句、让步状语从句和比较状语从句，共9种。一、时间状语从句引导时间状语从句的连接词有when，as, while, after, before, since, ever since, till, until, once, whenever, as soon as, no soonerthan, hardlywhen, the moment/minute/second/instant, directly, immediately, instantly, every time, each time, next time, by the time等。1. when, while, as引导的时间状语从句1) when的用法when既可引导一个持续性动作，也可引导一个短暂性动作，可用于主句和从句动作同时发生或主句动作先于从句动作。I was thin when I was a child. 当我是个孩子的时候我很瘦。The film had been on when we arrived. 当我们到达时，电影已经开演了。when引导时间状语从句时，如果主从句主语相同，从句有be动词，则从句可省略主语和be动词。When (you are) in trouble, you can visit this man. 当有麻烦时，可以找这个人。When (he was) a young man, he was fond of hunting. 他年轻时，喜欢打猎。when在be about to dowhen, be doingwhen, be on ones waywhen, be on the point of doingwhen,等结构中，当“这/那时”讲时，表示某件事正在发生或刚刚发生，另一动作同时发生。 I was about to go out when it began to rain. 我正要出去，这时天开始下雨了。The telephone was ringing when I got home. 当我到家时，电话铃正在响。2) while用法while引导的动作必须是持续的，强调某一时间段内，主从句动作同时发生，相当于during the time that。My mother was cooking while I was doing my homework. 当我在做作业时，妈妈在做饭。Please dont talk so loud while others are working. 别人在工作时，请别高声谈话。while除了可以用作从属连词之外，还可用作并列连词，表示对比关系“而，然而”。I like watching TV while he likes reading. 我喜欢看电视而他喜欢读书。3) as的用法as引导时间状语从句时，强调并行发生，不指先后。As I left the house, I forgot the key. 我离开家时，忘记了钥匙。as还可以说明两种正发展或变化的情况，有“随着”的意思，表时间的推移。As I get older, I get more optimistic. 随着年龄的增长，我变得更乐观。as常用作“一边一边”。He hurried home, looking behind as he went. 他匆忙回家，边走边往后看。John sings as he works. 约翰一边工作，一边唱歌。强调两个动作紧接着发生。As he was going out, it began to rain. 当他出去的时候，天开始下雨了。as有时引起一个名词，这时它相当于一个时间状语从句。As a boy (when he was a boy), he was hopeless at maths. 当他是孩子时，已对数学失去希望。2. before引导的时间状语从句1)before引导的时间状语从句，不用否定式的谓语。Before they got to the bus stop, the bus had gone.在他们到达公共汽车站之前，公共汽车已经走了。2)当before引导的从句位于主句之后时，译成“之后，才”，“在之前”，“还没来得及就”，“就，便（主句否定）”。如果主句中用一般将来时，before从句要用一般现在时代替一般将来时。It will be long before we meet again. 我们要过好久才能见面。Three weeks went by before she realised her mistakes. 三周过去了，她才意识到自己的错误。The war lasted four years before the north won in the end. 在北方取得最后胜利之前，战争持续了四年。He had hung up before I could answer the phone. 我还没有来得及接电话，他就挂断了。We hadnt waited long before the bus came. 我们等了不久公共汽车便来了。3. until和till引导的时间状语从句until和till都表示“直到”，常可换用，但till 不用于句首，也不可用于强调句。1)“延续性动词(肯定式)+until”表示动作延续到为止，译为“直到为止”。You may stay here until the rain stops. 你可在这里待到雨停。He waited until (it was) ten oclock. 他一直等到10点钟。I waited for him until he came back. 我一直等到他回来。2)“终止性动词/延续性动词的否定式+until”表示“直到才”。He didnt go to bed until he had finished his work. 他直到完成工作才睡觉。They didnt reach the village till it was dark. 他们直到天黑才到达那个村庄。He didnt come until he had gone over his lessons. 他一直到复习完了功课才回来。3)用于强调句式“It is not untilthat”。It was not until the professor came that we began the experiment.、在教授到来之后，我们才开始实验。4)not until放在句首时，主句要用倒装语序，如：Not until he graduated did he succeed in obtaining the compound.直到毕业他才成功获得这种化合物。4. since引导的时间状语从句since引导时间状语从句，意为“自从以来”，主句要用完成时态，但时间的计算方式略有不同。1)since后如果是终止性动词的过去式，则时间的起点应从该动作发生时算起。Mr Li has been here since he came back. 自从李先生回来之后，他一直在这儿。I have written home but once since I came here. 自从我到来这儿以来，只给家里写了一封信。2) since后如果是延续性性动词的过去式，则时间的起点应从该动作结束时算起。He hasnt been back at school since he was ill. 自从他病愈后一直没到学校来。I havent heard from him since he lived here. 自从他不住在这儿以来，我就没有收到过他的来信。3)有时时间的起点要从该动作发生时或状态开始时算起，主要根据句子的意思来考虑。Ive known Mr Smith since I was a boy. 我小的时候就认识史密斯先生了。4)在“It is +一段时间+since”句型中，时间一律以since从句的动作完成时算起。Its two years since we arrived here. 我们到这儿两年了。It was years since I had known her. 我认识她好几年了。It is three years since she was not in our class. 她离开我们班有三年了。5.表示“一就”的句型1)as soon as, once, immediately, directly, instantly, the moment/the minute/the second/the instant等引起的从句都表示从句的动作一发生，主句的动作就随即发生，常译作“一就”，这类从句中，经常用一般时态代替将来时态。As soon as he arrives, Ill tell him. 他一到，我就告诉他。Once you study hard, youll pass the exam. 你一旦努力学习，就会通过考试。The moment he comes, Ill let you know. 他一来，我就告诉你。The instantt I saw him, I recognized him. 我一看到他，就认出了他。 Well leave the minute you are ready. 你一准备好，我们就出发。I left immediately the clock struck 5. 我刚走，钟就敲了五下。2)on /upon+doing /n.作时间状语，译为“一就”。On arriving at the station, the thief was arrested. 一到车站，这个小偷就被逮捕了。On his arrival at classroom, the teacher came. 他刚刚到教室，老师便进来了。Upon his arrival in Paris, he was recognized as a noble and thrown into prison.他一到巴黎，就被认为是一个贵族，并被投进监狱。3)no soonerthan, hardlywhen, scarcely when/before引导的时间状语从句表示“刚就”“一就”。在这些结构中，主句动作先发生，用过去完成时，从句用一般过去时，主句常用倒装语序，把助动词had放在主语前面。I had no sooner reached the bus stop than the bus started. 我刚到车站车就开走了。I had scarcely/hardly entered the room when the phone rang. 我一进屋，电话就响了。注：当这些表示否定意义的词位于句首时，句子要倒装。No sooner had he reached home than it began to rain. 他刚到家，天