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When, before, since 句型1. when 的句型(1) be doing sth….when…正在做某事时…突然…We were swimming in the pool when it began to rain.We were studying English when he came in.(2) be about to do sth…. when …正要做…突然…We were about to leave when he came in.(3) had hardly/scarcely/just done sth…. when…刚…就…We had hardly finished the work when he came in.(4) when=now=since 表示“既然”It was foolish of you to take a taxi when you could get there in 5 mins. Now you are here, you’d better stay.2. before 句型(1) it will be + 时间段+ before sb. do sth. 再过多久…才…It was +时间段+before sb. did sth. 过了多久…才…It won’t be long before sb. do sth. 过不了多久某人就会…Eg. It will be 1 year before we go to college.It was 4 years before we graduated.(2) 主语+had done/did sth.+时间段+ before +did sth. 过了…才e.g. We had sailed for 4 days before we found the island.We waited a long time before the train arrived．我们等了很长时间火车才到。
before的用法是很多的人都比较想要了解的，在众人的心中before的用法是比较难的，我们都非常想要去了解before的用法，但是又谈何容易呢?为了让大家更加快速的了解before的用法，下面我们就和教师一起去看看吧，希望对大家有所帮助。
prep.在……之前;先于，优于;当着……的面;与其……conj.在……之前;在……以前;比……早些;与其……adv.先前，从前;在前，在前方before一词含义广泛，是高考考查的热点词汇之一，但部分考生对该词的用法模糊不清。
为了帮助大家掌握，现就对before的用法归纳如下：一、before用作连词1. before用作连词时，意思是“在……之前;还没来得及…… 就”。
强调主句或从句谓语动词表示的动作发生得过早或过快｡例如：Before she could move, she heard a great noise, which grew to a terrible roar. 她还没来得及动弹，就听见有很响的声音，接着就成了可怕的隆隆轰鸣声。
Before I could say a word, she had stormed out of the room. 不等我说一句话，她就冲出了房间。
Don’t count your chickens before they are hatched. 不要高兴得过早。
I must finish my homework before I watch TV.我必须做完作业才能看电视。
It still took seven years before they finally got married. 过了七年他们才最终得以成婚。
It will be only a few minutes before she comes back. 她过几分钟就会回来。
He announced the ending of the meeting before I could get in a word. 没容得我插上一句话,他就宣布散会了｡Someone called me up in the middle of the night, but they hung up before I could answer the phone.有人半夜给我打电话,但我还未来得及接他就把电话挂断了｡They had talked only a few minutes before they found they were quite different in opinion.他们才谈了几分钟就发现他们的意见很不一致｡注意：before从句若是一个将来的动作，则用一般现在时代替一般将来时，如上句中的comes。
It+be+ ⋯⋯ +that/since/before/when 用法辨析1. it was+ ( 时刻，或时间点） + when sth. happened. 当某事发生时，是几点钟或哪一年如：It was 1997 when Hongkong returned to China.It was five o'clock when we arrived at the small mountain village.对比强调句型： It was at five o'clock that we arrived at the small mountain village.It+ is/ was+ ⋯+that ⋯多用于强调。
判断方法如下：去掉 it 、be 和 that ，余下的部分仍是一个完整的句子，这样的句子一定是强调句。
2. it was+ 一段时间 + before sth happened.过了一段时间之后，某事才发生了。
如：it was two years before Macao returned to China.it will be +一段时间before sth. happens.要过一段时间之后，某事才会发生。
或不用过多久，某些就将发生：it won't be long before sth. happens.It won ’t be long before you see him again.没过多久就⋯It was long before they escaped from the prison.过了很久才⋯.3.it is (=has been)+ 一段时间 since sth. happened. 自某事发生以来，（时间）已经过去。
了。
如： It is 11 years since Hongkong returned to China. 香港回归已经有11 年了。
时间状语从句before 和since的用法before 和since的用法1.连词before表示“还未...就...；不到...就...；...才...；趁...还没...”Before they reached the station, the train had gone.他们(还没)到达火车站前，火车已经开走了。
We hadn’t run a mile before he felt tired.我们跑了还不到一英里他就累了。
Please write it down before you forget it.趁你现在没忘把它记下来。
2.before的句型：It will be +时间段+before从句，表示“多久之后才”。
It won't be long +before从句，表示“不久之后将...”It will be half a year before I come back.半年后我才回来。
(一般现在时表将来)It won’t be long before we meet again.不久后我们将再见面。
3.since的句型：It is/has been+时间段+since从句。
若从句的谓语为非延续性动词，表示“自从动作开始以来有多久了”；若从句的谓语为延续性动词，表示“自从动作结束/完成...有多久了”，常译为“自从不...有多久了”。
It is three years since the war broke out.战争爆发以来，有三年了。
It is twenty years since I've seen her. 我已经二十年没见她了。
五、every time, each time, next time, the first time, any time, all the time 的用法这些短语用来引导时间状语从句，表示“每当..；每次...；下次...”等。
掌握before 的用法一、 before用作连词1. before用作连词时，意思是“在……之前;还没来得及…… 就”。
例如：Before I could say a word, she had stormed out of the room.不等我说一句话，她就冲出了房间。
Don’t count your chickens before they are hatched. 不要高兴得过早。
2. 用于It + be + 时间段 + before...句型中，意思是“过多久---才……”。
如果主句中用否定式，则表示“不久……就”。
例如：It will be five years before I come back.我五年后才能回来。
It was not long before the enemy was driven out of their country.不久之后，敌人就被赶走了。
It won’t be long before they understand e ach other.他们不久就会互相了解的。
3 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，表“才”We had sailed four days and four nights before we saw lands.4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，表“不到---就”We hadn’t run a mile before he felt tired.5. 还有“趁……(还没有)”之意。
例如：They are thinking of buying the house before the prices go up.他们正在考虑趁房价未涨时把房子买下来。
Do it before you forget it. 趁早动手，以免忘了。
5. 有时还有“宁愿”的意思Eg: I would rather die before I apologized to him.二、before用作介词before用作介词时, 可以指时间“earlier than在……之前”，也可以指位置“in front of在……之前”。
句型意义备注It will/won’t be+ 时间段+before…要等多长时间才……/过不了多长时间就……It was/ wasn’t + 时间段+before…过了多长时间才……/没过多长时间就……It is/has been + 时间段+since 自从……以来已经有多长时间了1.从句中用短暂性动词表示动作持续了多久2.从句中用延续性动词表示动作结束了多久3.从句要用一般过去时It will be two years before he comes back from abroad. 要等两年他才回国。
It won’t be two years before he comes back from abroad. 过不了两年他就回国。
It was two years before he came back from abroad. 过了两年他才回国。
It wasn’t two years before he came back from abroad. 没到两年他就回国了。
It is/has been two years since he came back from abroad. 他回国已经两年了。
It is/has been two years since he lived abroad. 他不在国外已两年了。
How long do you think it is _________ he arrived here?-- No more than half a year, I believe.It was two years later _______ he came back from abroad.It is two hours ______ he spends on English every day.It was at 6 o’clock _______I got up today.It was 6 o’clock _______ I got up today.1. It is / was (high / about) time +(that)… “是做……的时候了”，从句的谓语动词用：①过去式（be用were）② should+ 动词原形，should 不可省,表示虚拟语气。
答：一、掌握before热点用法1. prep. 在......以前，强调时间He came to see me the day before yesterday. 他前天来看我了。
2. prep. 在......前面，当着......的面，向......，强调地点She has to appear before the court. 她必须出庭受审。
3. prep. 在......之前，先于，强调次序Those with babies can get on the bus before others. 带小孩的人可以先上汽车。
4. prep. 与其......（宁愿）I'd shoot myself before I apologized to him! 我宁死也不向他道歉!5. adv. 以前，强调时间We've seen that film before. 我们以前看过那场电影。
6. adv. 在前面，向前，强调位置Don't run before and after. 别跑前跑后。
7. conj. 在......前，强调时间before的含义比较灵活，实际翻译时应结合具体情况机动处理。
1. 趁......You should do it before it is too late. 趁现在还不算太晚，你应该赶快做它。
2. 尚未来得及Before she could move, she heard a loud noise, which grew to a terrible roar. 她还没有来得及动弹，就听见有很响的声音，接着就成了可怕的隆隆轰鸣声。
Before they reached the house, a new great wave came, sweeping down trees, and sweeping them down too. 他们还没到屋子，又一个巨浪打来，冲倒了树，也冲倒了他们。
9.before 句型：
(1) It will be +时间+ before + 还有多长时间……
例：It will be 4 years before he graduates. 他还有四年时间就毕业了。
(2) It was +一段时间+ before 过了多久就……
例：It wasn’t two years before he left the country. 还没到两年他们离开了那国家。
(3) before sb can/ could … 某人还没来
得及……
例：Before I could get in a word ，he had measured me．
(4) 过了多久才……
例：We had walked a long way before we found some water.
（5）还有“趁……（还没有）”之意。
例如：They are thinking of buying the house before the prices go up.
(6) before long是“很快，不久”的意思, 可以用于各种时态。
Before long, he went to America.
(7) long before是“很久以前”的意思
Eg: That happened long before. 那件事发生在很久以前。
They had known each other long before they got married.
10. since 句型：
It is/ has been +时间段+ since…+一般过去时. (到目前为止）干某事有多长时间了
It was + 时间段+ since +过去完成
时（到过去某时间为止）干某事有多长时间了
Sb/ sth.+ 现在完成时+since+ 过去时。
（注意从句的谓语动词是否延续）
Eg: It is about ten days since he came back from abroad.
It was days since I had left there.
比较一下：
He has written to me frequently since I fell ill. 自从我生病以来，他就经常给我写信。
He has written to me frequently since I was ill. 自从我病愈以来，他经常给我写信。
11. when 句型：
It will be +时间+ when +一般现在时当某事发生时，时间将会是。
It was +时间+ when+一般过去时当某事发生时，时间是。
Eg: It will be midnight when they get there .
It was 1949 when new China was founded.。
