状语从句中“when while as soon as before”等引导词的区分.

状语从句中“when while as soon as before”等引导词的区分.

when 作为从属连词,引导状语从句,表示多种语法意义:1.表示时间,意为“当……时;在……的时候”.A.在时间、条件等状语从句里,用一般现在时表示将来时;当需要表达将来完成的意义时,必须使用现在完成时来代替.如:( 1 ) When you see him,please say hello to him.见到他时,代我问他好.( 2 ) When you have finished your experiment,please tidy the lab and put everything back in the cupboards.当你们做完实验后,请把实验室整理好并把物品放回柜子中.B.表示过去发生的事情,在 when 引导的时间状语从句的主从复合句中,动作发生在先的用过去完成时,在后的用过去时.如:( 1 ) When I was in Japan,I bought some beautiful pearls.我在日本时,买了一些漂亮的珍珠.( 2 ) When I reached the station,the train had left.当我到达火车站时,火车已经开走了.2.表示前面的叙述所没有提到过的信息.它总是对所描述的事件予以引人注目的强调,意为“这时;突然”;当位于句末的分句具有引种用法时,大致有以下三种情况:A.when 分句前面的分句使用过去进行时.如:( 1 ) He was still smiling when the door opened and his wife came in.他正笑着的时候,门突然开了,他妻子走了进来.( 2 ) I was thinking of this when I heard my name called.我正想着这件事时,突然听到有人叫我的名字.B.when 分句前面的分句使用 was (were) about to,was (were) on the point 等.如:( 1 ) We were about to start when it began to rain.我们刚要出发就开始下雨了.( 2 ) He was on the point of leaving when someone knocked at the door.他刚要走就有人敲门.C.when 分句之前的分句用过去完成时,其中 sb had hardly / scarcely /barely … when 已成为固定词组.如:( 1 ) We had hardly fallen asleep when the bell rang.我们刚刚入睡,铃声就响了起来.( 2 ) He had scarcely arrived when he had to leave again.他刚刚到达就又要离开了.3.表示条件,相当于 if ,引导条件状语从句.如:How can I get a job when I can't even read or write?如果我连读和写都不会,我怎么能找到工作呢?4.表示对比,主要有以下两种情况:A.相当于 whereas,while,since,意为“既然;然而”.如:( 1 ) How can I help them to understand when they won't listen to me?既然他们不愿听我的,我又怎么能帮助他们弄明白呢?( 2 ) They have only three copies when we need five.他们只有三本,而我们却需要五本.B.when 从句中使用虚拟语气,意为“本来……却……”.如:( 1 ) She paid when she could have entered free.本来可以免费入场,而她却付了款.( 2 ) She stopped trying when she might have succeeded next time.她本来下次有可能获得成功,但她却不再尝试了.( 3 ) They were gossiping,when they should have been working.他们本该工作,却在那里说别人的闲话.5.由 w hen 等引导的状语从句,如果主语与主句的主语一致或是 it ,谓语动词又含 be 动词时,主语和 be 动词常常被省略,就变成“ when + V-ing/ V-ed/ adj/ 介词词组”的结构.如:( 1 ) When in Rome,do as Romans do.入乡随俗.( 2 ) When (we are ) young,we are full of hope.年轻时,我们大家总是充满希望.( 3 ) Don't reach sideways when standing on a ladder.站在梯子上时,不要侧着身子去够东西.while (1)引导时间状语 1.We must strike while the iron is hot.趁热打铁.2.While she was listening to the radio,she fell asleep.她听着收音机睡着了.(2)引起让步状语从句,意思是“虽然…但是….”、“尽管…但是…”(多放于句首)1.While he loves his students,he is very strict with them..虽然他爱他的学生,可是他对他们很严格.2.While these experiments are interesting and useful,it is important to remember that they may not always tell us much.(BookIIIp125) 虽然这些实验很有趣也有用,但是很重要的是要记住,这些实验也可能不会告诉你很多.(3)引起条件状语,意思是“只要” 1.While there is life there is hope.只要生命存在,就有希望.2.While there is a way there is away.有志者事竟成.as soon as before as soon as连接的时间状语从句中,指未发生的动作,规律是：主句一般将来时,从句用一般现在时代替一般将来时 如：I will tell him the news as soon as he comes back.指紧接着发生的两个短动作,主从句都用一般过去时 如He took out his English books as soon as he sat down 就这两种情况 ,熟记就行.在宾语从句中,当主句为与过去时的时候,从句必须用与主句相对应的时态,所以为了与主句动词said呼应,时间状语从句中的will look up应该对应为过去将来时态would look up,finds对应为found