before after when and while的用法

before after when and while的用法
before after when and while的用法

before after when and while的用法
when作并列连词构成并列句,意为and at that time“正在那时”,and just then“那时”或and then“突然”等意思.when前可以用逗号,也可以省略.同时,when可与suddenly连用以加强语气.这种结构常常用来表示发生的事情带有意外的性质.其句型有三类：
　　1.sb.was doing sth.when （suddenly）...表示“某件事情正在进行时,另一件事也发生了”.
　　We were swimming in the lake when suddenly the storm started.我们正在湖里游泳,这时突然下起了暴风雨.
　　2.sb.was （just） about to do...when （suddenly）...表示某人刚要开始做某事,（突然）另一件事发生了.
　　he was about to tell me the secret when someone patted me on the shoulder.他刚想把这秘密告诉我,这时某个人拍了拍我的肩膀.
while 用作连词时,有以下几种含义：
1.意为“当……时候,和……同时”,引导时间状语从句.例如：
While I was watching TV,the bell rang.
我看电视时,铃响了.
Meimei watched TV while she ate her supper.
梅梅边吃晚饭边看电视.
2.意为“虽然,尽管”,引导让步状语从句.例如：
While it was late,he went on working.
虽然很晚了,但他还在继续工作.
While he is in poor health,he works hard.
虽然他身体不好,但他还是努力工作.
3.连接两个并列句子,表示“对比”关系.例如：
He went out for a walk,while I stayed at home.
他出去散步了,而我却呆在家里.
I like singing while she likes dancing.
我喜欢唱歌,而她喜欢跳舞.
You like sports,while I prefer music.
你喜欢体育,而我更喜欢音乐.
after的用法：
after引导的时间状语从句如果具有将来意义,往往要用一般现在时来表示(有时也用现在完成时),而不能直接用一般将来时.如：
误：I’ll tell him after you wil leave.
正：I’ll tell him after you leave (或have left).你走了之后我再告诉他.
(2) 选择一般现时或现在完成时(表示将来意义)的基本原则是：如果强调从句 动作在主句动作之前完成,则用现在完成时；如果强调主从句动作　同时发 生,或几乎同时发生(尤其是当从句的谓语动词是get,arrive,see,hear,leave,return等表示迅速完成的动作的动词时),多用一般现在时(有时 两种时态都可以).如；
I’ll leave when he comes back.他回来后我就离开.
I will give my opinion when I have read the book through.我把书看完了再提意见.
We’ll leave as soon as it stops (或has stopped) raining.雨停我们就动身.
2.一般说来,如果在过去某一时间内先后发生了两个动作,那么先发生的动作用过去完成时,后发生的动作用一般过去时.但是若用连词after 来连接这两个动作,由于after本身已说明了两个动作的先后关系,所以两者均可用一般过去时.如：
After he (had) closed the door,he left the house.关了门之后,他就离开了家.
3.有时以连词after引导的时间状语从句可以换成一个以介词after引导介词短语或以连词after引导的分词短语,而意义不变.如：
He went to school after he had breakfast (=after breakfast).吃了早饭之后,他就去上学了.
After l had finished (=After having finished / After finishing / Having我干完活后就去睡觉了.
4.after还可用作副词,意为“后来”或“(一段时间)以后”,通常要放在另一时间副词之后.如：
We arrived soon (或just / shortly) after.我们不久就到了.
He returned twenty years after.20年后他回来了.
before的用法
1.表示“在…..之前就…..”.
Mary had finished her homework before her mother returned.
2.表示“过了多久后才……..,动作进行到什么程度才……”
The man almost knocked me down before he saw me .
They walked about 30 miles to the west before they saw a village .
They worked day and night about three days before everything returned to normal .
3.表示“刚…就…”
I had hardly sat down before the bell rang.
4.表示“不知不觉就…..； 还没弄清就……”
Time passed quickly and three months went by before Aqiao knew it.
5.用于句型“it was +时间段+ before …” 表示 “过了多久才…”
It was three days before he came back..
6.用于句型“ it was not long +时间段+ before …” 意为“不久就….”
It was not long before he sensed the danger of the position .
7.用于句型“it will be(not )+时间段+ before….”表示“要过多久/ 不久…才…”
It will be half a year before you graduate from this school .
It will be not long before you find you are wrong .

before的用法
一、可以用作介词
⒈)指时间上早于，在……之前，如：
She has lived here since before the war.
她从战前就一直在这儿住。
⒉)指位置在前面，如：
We knelt down before Grandma‘s grave.
我...

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before的用法
一、可以用作介词
⒈)指时间上早于，在……之前，如：
She has lived here since before the war.
她从战前就一直在这儿住。
⒉)指位置在前面，如：
We knelt down before Grandma‘s grave.
我们在奶奶的墓前跪下。
⒊)指顺序或排列在之前，如：
Your name comes before mine on the list.
名单上你的名字在我之前。
⒋)在某人面前，如：
She said it before the witness.
他是当着证人的面说的。
二、作为连词
其基本含义是“在……之前”，又可以根据不同语境灵活翻译成“才”、“还没来得及就……”、“趁……”、“就”等。具体用法如下：
⒈)与情态动词can/could连用
这时候从句虽为肯定形式，根据汉语表达习惯译成“还没来得及就”，如：
Before I could get in a word，he had measured me.
我还没来得及插话他就为我量好了尺寸。
Before she could move，she heard a loud noise，which grew to a terribl eroar.
她还没来得及迈步，就听见一声巨响，接着就是可怕的隆隆轰鸣。
⒉)用于肯定句中强调主句所表达的时间，距离长，或花费的精力大，译成“才”
We had sailed four days and four nights before we saw lands.
我们航行了四天四夜才看到陆地。
We waited a long time before the train arrived.
我们等了很长时间火车才到。
⒊)用于否定句中，强调主句所表达的时间，距离短，或花费的精力小，译成“不到……就”如：
We hadn‘t run a mile before he felt tired.
我们跑了还不到一英里他就累了。
⒋)主句含有hardly，scarcely等半否定副词时可以译为“刚……就”
这时候主句应用过去完成时态，从句用过去时，还可以用when替代before如：
We had scarcely reached the school before/when the bell rang.
我们刚到学校铃声就响了。
⒌)有时还有“宁愿”的意思
I‘d shoot myself before I apologized to him.我宁死也不向他道歉。
⒍)用于It+be/take+时间段+before句型
在这一句型中又可以根据主从句的时态分成两种情况。
若主句是一般时将来时态，从句是一般现在时.若主句是肯定句意思是“要过多长时间才”；若主句是否定形式翻译成“用不了多久就”。
It will be two weeks before everything returns to normal.
两周之后一切才能恢复正常。
It will be many years before the situation improves.
这种状况或许要过许多年才能得以改善。
It won‘t be long before we meet again.用不了多久我们就会再见面的。
这时若主句是一般过去时从句也是一般过去时。若主句是肯定句翻译成“多长时间之后才”，若主句是否定形式翻译成“没过多久就”。如：
It was some time before I realized the truth.
过了很长一段时间我才了解到真相。
It wasn‘t long before she became a brave solider.
没过多久她就成了一名勇敢的战士。
After that it still took seven years before they got married.
他们又过了七年才结婚。
注意：当主句的谓语动词为延续性动词时，before与until有时可以互换。It was an hour before/until the police arrived.
after的用法
(1)介词:
(a) Please come to my house after dinner.晚饭后
(b) He ran after the bus. 追赶
(c) His mother waited for him night after night.（一个）接着（一个）
(d) It's sad to fail after all that work. 由于
(e) They are still friends after all their differences.
(2) 副词:
(a) three hours after; (b) departed shortly after; (c) after all I don't really know him. 终究
(d) He told me afterwards that he had not enjoyed the film. 后来
(3)连词:
(a) I saw them after I arrived.后来
(b) They arrived soon after. 后来
(c) tomorrow, or the day after...
(4) 名词:
(a) afternoon午后; (b) afterthought事后的想法; (c) aftermath后果
when的用法
副词 ad.
1.(用作疑问副词)什么时候,何时
I'd like to know when they'll let him out.
我想知道他们什么时候放他。
When did you last see Margaret?
你上一次见到玛格丽特是什么时候?
2.(用作关系副词,引导关系从句)当...时
There were times when I didn't know what to do.
有些时候我不知道该怎么办才好。
连接词 conj.
1.当...时
John got engaged to her when travelling last winter.
去年冬天旅行时,约翰与她订了婚。
Don't get excited when you talk.
你说话时别激动。
2.既然,考虑到
How can he get the promotion when his boss dislikes him?
既然上司不喜欢他,那他怎么会获得提升呢?
3.虽然,然而
I had only fifteen dollars on me when the book I wanted cost twenty.
我身上只带了十五元钱,可是我想买的那本书定价二十元。
4.在那时,然后
代词 pron.
1.什么时候,那时
Since when has she taught here?
她从什么时候开始在这儿教书的?
名词 n.
1.(事件发生的)时间[the S]
while的用法
名词 n.
1.一会儿,一段时间[S]
I'll be back in a while.
我一会儿就回来。
连接词 conj.
1.当...的时候,和...同时
She listened closely while he read the letter.
他读信时,她听得很仔细。
I'll take care of your children while you are away.
你不在时我会照顾你的孩子的。
We must strike while the iron is hot.
我们必须趁热打铁。
2.而,然而
I like tea while she likes coffee.
我喜欢喝茶,而她喜欢喝咖啡。
3.虽然,尽管
While I like the color of the hat, I do not like its shape.
虽然我喜欢这顶帽子的颜色,但我不喜欢它的形状。
4.只要
及物动词 vt.
1.消磨(时光),轻松地度过[(+away)]
He whiled away

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