it was+ 一段时间+since还是before从句

高考It +be+ 时间+ 从句”结构总结一在“It +be+ 时间+ 从句”结构中，引导从句的从属连词有before, that, since, until （till ）, when 等。

这一结构是近几年高考常考的知识点，现将它们的用法小结如下：一、It +be （not ）+ 时间段+before 从句。

其中的主句是肯定式时，意为“过多长时间才……”；主句是否定式时，意为“没过多久就……”。

例如：1. It was not long before the whole country rose and drove the Austrian soldiers from their homeland. 不久，全国人民便奋起反抗，把奥地利军队从他们的国土上赶了出去。

2. It may be five or six years before the new medicine is tested on human beings.要过五六年时间这种新药才能在人身上做试验。

3. It was two months before he designed the bridge. 过了两个月，他设计出了这座桥梁。

二、It +will be （was ）+ 时间段+until 从句若主句中用一般将来时，则从句中用一般现在时，意思是从现在起到从句中谓语动词表示的动作发生时还有多长时间；若主句中用一般过去时，则从句中也用一般过去时，意思是从过去某一时间起到从句中谓语动词表示的动作发生还有多长时间。

例如：1. It will be ten days until my birthday comes. 到我生日还有十天。

2. It was only five minutes until her husband came back from work.当时离她丈夫下班只有五分钟了。

注意：结构“一”与结构“二”在肯定句中几乎可以通用。

It is +一段时间+since…的句型与It has been +一段时间+since…意思相同，since从句用现在完成时。

前者是规范说法，后者是口语说法。

It was+一段时间since从句就用过去完成时。

一、若since引导的状语从句的谓语动词是终止性的过去时He has studied very hard since he came to our school.自从他来到我们学校，他学习就非常努力。

We have been missing them since they left here自从他们离开这里，我们就一直很想念他们。

It has rained a great deal since you left.你走之后下了好多雨。

We have resided in Shanghai since we parted.自从分手以后，我们一直住在上海。

这是最常见的一种用法，此处不再多述。

二、若since引导的状语从句的谓语动词是延续性动词或表示状态的动词的过去式时I haven’t heard any noise since I slept.这句应译为“我醒后还未听到任何声音”。

John is now with his parents in New Y ork, it is already three years since he was a teacher约翰现在和父母一起住在纽约，他不当教师已经三年了。

It's two years since I smoked我戒烟已经两年了。

How long is it since you lived in Shanghai?你离开（没住在）上海多久了？It is half a month since he was a League member.他退团（不当团员）半个月了。

It’s been quite some time since I was last in London我离开伦敦已很长时间了。

storm started.
AA.. wwhen
B. while C. until
D. before
2. (02上海) He was about to tell me the secret ______ someone
patted him on the shoulder.
A. as
B. until
C. while D. whheenn
when,before,since句型归纳
1、when 句型： (1) be doing sth…when…
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) be about to do sth…when… We were about to start when it began to rain. 我们刚要出发，天就开始下雨了。
It is 5 years since he left Beijing . 他离开北京5年了
It has been 3 years since he came back from abroad.自从他回国已经三年了
3.since句型
It is/has been＋时间段＋since sb. did… §②§did动作为持续动词（延续性），翻译为 自从不做某事有多长时间
(4)hardly /sceracely…when… (一…就…) He had not/hardly/scarcely fallen asleep when the telephone rang. 他刚要入睡电话就响了。
We had scarcely arrived when he asked us to leave. 我们才刚刚到他就叫我们走了.

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。

(3) 若since引导的状语从句的谓语为持续性动 词或静态动词的现在完成时， 则表示动作和 状态延续到现在(说话时刻)， 其表示的时间的 起点应从动作发生之时算起。如：
He has written to me frequently since I have been ill.
have been ill表示状态的持续性（理解时注意 与⑴区别）， 时间的起点应从：“开始生病” 时算起。因此此句可理解为：“自从我生病以 来， 他经常给我写信。”
试比较翻译：
I've written her 20 letters since I have been here. (从开始算起)
I've written her 20 letters since I was
here. (从结束算起)
(4) It is + 段时间 + since... / It has been + 段 时间 + since...表示“从……起已有多长时间 了”。
I haven't heard from him since he lived here.
这句话应译为：从他不住这儿起， 我一直没有收
到他的信。
I haven't eaten snakes since I was a student at
school.
was表示状态，因此该句可理解为：I haven't
A. when B. that C. before D. since
2. It was some time _________we realized the truth. (山东卷)
A. when B. until C. since

高考It +be+ 时间+ 从句”结构总结一在“It +be+ 时间+ 从句”结构中，引导从句的从属连词有before, that, since, until （till ）, when 等。

这一结构是近几年高考常考的知识点，现将它们的用法小结如下：一、It +be （not ）+ 时间段+before 从句。

其中的主句是肯定式时，意为“过多长时间才……”；主句是否定式时，意为“没过多久就……”。

例如：1. It was not long before the whole country rose and drove the Austrian soldiers from their homeland. 不久，全国人民便奋起反抗，把奥地利军队从他们的国土上赶了出去。

2. It may be five or six years before the new medicine is tested on human beings.要过五六年时间这种新药才能在人身上做试验。

3. It was two months before he designed the bridge. 过了两个月，他设计出了这座桥梁。

二、It +will be （was ）+ 时间段+until 从句若主句中用一般将来时，则从句中用一般现在时，意思是从现在起到从句中谓语动词表示的动作发生时还有多长时间；若主句中用一般过去时，则从句中也用一般过去时，意思是从过去某一时间起到从句中谓语动词表示的动作发生还有多长时间。

例如：1. It will be ten days until my birthday comes. 到我生日还有十天。

2. It was only five minutes until her husband came back from work.当时离她丈夫下班只有五分钟了。

注意：结构“一”与结构“二”在肯定句中几乎可以通用。

It …+点时间/段时间+before…诠释高中英语中,before句式,相似性强,考生易混淆,究其用法,现小结于后,敬供商榷;1. It was / will be + 段时间+ before …在“It was / will be + 段时间 + before 从句”结构中,before是从属连词,表示“……才；……就”,引导时间状语从句;例：It was just 3 days before the book was published.三天后那本书就出版了;例：It will be five years before we meet again.五年后我们才会在见面;2. It wasn’t long before …/ It won’t long before …在“It wasn’t long before从句”结构中,before是从属连词,表示“不久以后就……”；而“It won’t long before从句”结构中,before是从属连词,意为“不久就会……”,引导时间状语从句;例：It wasn’t long before he came home.他不久后才很快回到了家里;例：It won’t long before you get well again.不久你就可以恢复健康了;3. It be + 点时间+ before …在“It be +点时间 + before从句”结构中,before是从属连词,表示“在……之前；时间是……”,引导时间状语从句;例：It was 4:00 before he came to see you.他是四点后来看你的;4. It be + 点时间+ when …在“It be +点时间 + when从句”结构中,when是从属连词,表示“当时是……”,引导时间状语从句;例：It was 4:00 when he came to see you.他来看你时,已是四点了;5. It be + 段时间+ since …在“It be +段时间 + since从句”结构中,since是从属连词,引导时间状语从句;若从句中谓语动词是短暂性动词,表示“自从……以来有多久了”；若从句中谓语动词是延续性动词,则表示“多久不……了”;例：It was two years since I joined the League member.我入团已三年了;join是短暂性动词例：It was many years since I enjoyed myself like this.我已有多年没有像这么开心了;enjoy是延续性动词6. It be + 时间+ that …在“It be +时间 + that从句”结构中,构成强调句,表示“就是……时间才……”;例：It was two years later that I came back from abroad.正是两年后我才回国的;7. It is / will be + 段时间+ until …在“It is / will be +段时间 + until从句”结构中,until是从属连词,引导时间状语从句,表示“过了要过多久才……”,until相当于before;例：It would be 10 years until / before he knew the truth.十年后他才得知真相;温馨提示1until用于肯定句,表示“直到……为止”,谓语动词一般是延续动词,常见的有stay, work, study, play等,表示动作一直延续到until所表示的时间为止;例：Tell him to stay up until I get back..告诉他,等我回来后再去睡;2until用于否定句,表示“在……之前；直到……才”,谓语动词一般是终止性动词,常见的有come, arrive, leave, die等,表示动作到until所表示的时间时才发生;例：They won’t come to any decision until they had a chance to discuss it wholly.等有机会全面讨论这个问题后才定夺;综合上述,句子结构千变万化,规则众多,用法奇特,但只要根据已有的学习经验和知识水平分析句子,理解用意,进一步进行信息整合,推理判断,便可找到更新的理解办法或途径,这样,无论多么难的句子都可以一一化解了;经典演练1. It was _____ he came back from Africa that year ____he met the girl he would like to marry.A. when; thenB. not; untilC. not until; thatD. only; when2. --- Have you know Dr. Jackon for a long time--- Yes, since she ____ the Chinese Society.A. has joinedB. joinsC. had joinedD. joined3. --- Did his father come back early last night--- Yes, it was not yet eight o’clock ___ he arrived home.A. beforeB. whenC. thatD. until答案与解析1. C 考查强调句与时间状语从句辨析;句意：正是他那一年从非洲回来时,他才遇到了他的确想要结婚的那位姑娘;此处应是强调句型,被强调的对象是“not until he came back from Africa that year ”,不是时间状语从句,而选项A,B和D项不合要求,故C项正确;2. D 考查since时间状语从句;句意：自她加入汉语协会以来;据语境分析,此处since表示“自从……以来”,而选项A,B和C均不合语义,故D项正确;3 B 考查when时间状语从句;句意：当他回到家里时,还不到八点;据语境分析,此处it指时间,when引导时间状语从句,表示“当……时候”,而选项A,C和D均不合语义,故B项正确;能力提升1. --- How long do you think it will be ____ China sends a manned spaceship to the moon--- Perhaps two or three years.A. whenB. untilC. thatD. before2. It was some time later ___ we realized two or three years.A. untilB. beforeC. thatD. since3. How long is it ___ we last saw each other in ShanghaiA. sinceB. beforeC. untilD. that4. That was really a special evening, it’s years ___ he enjoyed himself so much.A. whenB. thatC. beforeD. since5. It seemed only seconds ___ the boy finished washing his face.A. whenB. beforeC. afterD. since6. --- What did she want to know, Tom--- She wondered ____ we could complete the experiment.A. when was itB. it was when thatC. it was whenD. when it was that7. Was it in 1939 ___ the Second World War broke outA. thatB. whenC. untilD. since8. It was two years ___ I began to learn English.A. whenB. sinceC. beforeD. that9. It was not until dark ___ he found ___ he thought was the correct way to solve the problem.A. that; whatB. that; thatC. when; whatD. when; what答案与解析考查before时间状语从句;句意：--- 你认为中国多少时间后才能把宇宙飞船发射到月球上呢--- 或许两三年吧;据语境分析,此处before引导时间状语从句,表示“在……之前,……才”,而选项A,B和C均不合语义,故D项正确;考查强调句与时间状语从句辨析;句意：就是一段时间以后我们才能弄清事实的真相;据语境分析,此处强调“some time later”, It be …that …构成强调句式,而不是时间状语从句,而选项A,B和D均不合句式要求,故C项正确;考查since时间状语从句;句意：我们最后一次自在上海见面后有多长时间了呢据语境分析,此处应是since引导时间状语从句,表示“自……以来”,而选项B,C和D均不合语义,故A项正确;4. D 考查since时间状语从句;句意：那是一个特别的晚上,已有多年没有这么开心了;据语境分析,此处应是since引导时间状语从句,表示“自……以来”,而选项A,B和C均不合语义,故D 项正确;5. B 考查before时间状语从句;句意：好像没大一会儿,那个小孩就把脸洗完了;据语境分析,此处应是before引导时间状语从句,表示“….才”,而选项A,C和D均不合语义,故B项正确;6. D 考查强调句与时间状语从句辨析;句意：--- 她到底想知道什么,Tom--- 她想知道我们完成这项实验的时间;据语境分析,此处应是强调句,被强调的对象是“when”,又因放在she wondered之后,随之构成宾语从句,将when提出以平衡句子,表示“….时候”,而选项A,B和C均不合要求,故D项正确;7. A 考查强调句与时间状语从句辨析;句意：就是在1939年爆发的第二次世界大战吗据语境分析,此处应是强调句型,被强调的对象是“in 1939”,不是时间状语从句,而选项B,C和D均不合要求,故A项正确;8. B考查since时间状语从句;句意：我自学英语以来,有两年时间了;据语境分析,此处应是since引导时间状语从句,表示“自……以来”,而选项A,C和D均不合语义,故B项正确;9. A 考查强调句与时间状语从句辨析;句意：直到天黑时,他才发现他所想到的正是解决这个问题的有效途径; 据语境分析,此处应是强调句型,被强调的对象是“not until dark”,又在he found后跟了一个what引导的宾语从句,不是时间状语从句,而选项B,C和D均不合要求,故A 项正确;be +时间段＋before...过了多长时间才.：It was two days before he knew.过了两天他才知道.It was three years before he came back from abroad.过了三年他才从国外回来.be+ 时间点＋when...当.时候,时间是.：It was six when he arrived.当他到达时,时间是6点钟.is / has been +时间段＋since...往往用非延续性动词自从……以来到现在已有多久,做.已经多长时间了：It is / has been five years since he died.他已经死了5年了.is three years since they got married.他们已经结婚三年了.It is three years since they were married.他们已经离婚三年了.若since引导的状语从句的谓语动词是持续性动词或表示状态动词的过去时时,则从句表示的时间是“从动作或状态结束时算起”.再如:It has been quite some time since I was last in London.我上次离开伦敦至今颇有一段时间了. won't be long before...:不久.It won't be long before we meet again.我们不久会再见面.。

发生已经有3天了。）
It was+一段时间+since从句
• It was+一段时间+since从句 从句用had done）,主句用一般过去式.
• It had been+一段时间since 从句（did），主 句had done
• It was three years since Jack had been a teacher.
延续性v.,翻译时直译) • eg. It is 5 years since I have lived here. (live为延续性v.故直译为：自从我住在这儿已经5年了。) 2. it is/has been +时间段n.+ since sb. did(如v.为短暂性v./
瞬间性v. 翻译时直译,如为延续性v./表示状态词 翻译 时反译) It is 5 years since I lived here. （live为延续性v.故反译为我已经5年不住这儿了。） It is 3 years since I smoked. （smoke为延续性v.故反译为我已经3年不吸烟了。）
• It had been three years since Jack was a teacher.
• 杰克不当老师已有3年了
• 1）在 “It was + 一段时间 + before从句句型 中，若主句是一般过去式，从句也是一般过 去式时：
① 若主句是肯定句，翻译成“过了多长时间
之后才……” 例：It was long before they found their son. 过了很久他们才找到他们的儿子。
It is+adj+doing
It is + useless (nice, good，interesting, expensive等形容 词)+ doing sth． It is useless speaking.光说没用。

It is three years since I’ve seen him. = It is three years since I saw him.
since从句如为延续性动词，用一般过去时， 表示“动作的结束”。例如：
It’s years since I eபைடு நூலகம்joyed myself so much. It is four years since she was a nurse. How long is it since you were in London.
9. ----Did Jack come back early last night? ----Yes. It was not yet eight o’clock __b__ he arrived
home.
A. before
B. when
C. that until
10. Scientists say it may be five or six years __c__ it is
10.It was/will be+时间段+before... 该句型的is后可接long或一段时间。肯定句 译为“过多久…才…”；过了多久将会。。。 否定句译为“没多久…就…”。例如： It was a long time before I got to sleep again. It will be hours before he arrives here. It was not long before he left his home town. It will be five years before we meet again.
11．It is … since… 该句型表达“自从……以来已经多久了 It is 15 years since the war ended. It is just a week since we arrived here. It is ten years since he left his home town. It must be almost 5 years since we last met. 从句中可用现在完成时。例如：

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。

若从句中的动词是终止性动词，意为：“从开始……多久了”例如：It has been five years since she left home.(她离家已经十五年了）It was four years since he had died.（到当时为止，他已死去四年了）若从句中的动词是延续性动词，意为：“不做某事已有多久了”例如：It is two days since she was ill.（她病好了两天)It is two years since he studied English。

It 的用法1：it 做形式主语，不定式to do 或that 引导的句子做真正的主语例句: It is important for us to protect environment. 保护环境对我们来说是很重要的。

（it 做形式主语，真正的主语是to protect environment）即to protect environment is important for us 是本句，但这样显得头重脚轻，所以用it 做形式主语.例句: It is common knowledge that science and technology is the first productive force.( it 做形式主语，that 引导的句子做真正的主语2：it 做形式宾语，不定式to do 或that 做真正的宾语例句：He thinks it very hard to master a foreign language.他认为掌握一门外语是很难的。

（he 做主语，thinks 做谓语，it 做形式宾语，very hard 做宾补，to master a foreign language 做真正的宾语，即He thinks to master a foreign language very hard.例句：He thinks it very essential that he should have a decent job.他认为他应该有一份体面的工作是很必要的即He thinks that he should have a decent job very essential.3: it 用于强调句，其结构是it is \was+强调部分+that例句：It was his carelessness that caused his fatal failure.正是他的粗心导致了他的致命失败。

（强调his carelessness,做caused的主语,即强调主语）例句：It was in the cinema that I came across my former English teacher.在电影院我巧遇我的前任英语老师。

It …+点时间/段时间+before…诠释高中英语中，before句式，相似性强，考生易混淆，究其用法，现小结于后，敬供商榷。

1. It was / will be + 段时间+ before …在“It was / will be + 段时间 + before 从句”结构中，before是从属连词，表示“……才；……就”，引导时间状语从句。

例：It was just 3 days before the book was published.三天后那本书就出版了。

例：It will be five years before we meet again.五年后我们才会在见面。

2. It wasn’t long before …/ It won’t long before …在“It wasn’t long before从句”结构中，before是从属连词，表示“不久以后就……”；而“It won’t long before从句”结构中，before是从属连词，意为“不久就会……”，引导时间状语从句。

例：It wasn’t long before he came home.他不久后才（很快）回到了家里。

例：It won’t long before you get well again.不久你就可以恢复健康了。

3. It be + 点时间+ before …在“It be +点时间 + before从句”结构中，before是从属连词，表示“在……之前；时间是……”，引导时间状语从句。

例：It was 4:00 before he came to see you.他是四点后来看你的。

4. It be + 点时间+ when …在“It be +点时间 + when从句”结构中，when是从属连词，表示“当时是……”，引导时间状语从句。

例：It was 4:00 when he came to see you.他来看你时，已是四点了。

高考英语常考句式——it is +时间 + since (before, when)…请注意以下三个句式的区别和意思上的差异（其中的 is 根据情况可以有其他时态形式）：It is + 时间段 + since…的意思是“自从……以来有一段时间了”。

It is + 时间点 + when…的意思是“当……的时候时间是……”。

It is + 时间段 + before…的意思是“在……之前有一段时间”。

请看以下用例：It’s ten years since they got married. 他们结婚到现在已经十年了。

It was past one o’clock when he came in. 他回来时已经一点多了。

It won’t be long before they understand each other. 过不了多久他们就会互相了解的。

有时翻译可以比较灵活：It’s a long time since I met you last. 好久不见了。

(直译：自上次见到你以来有很长一段时间了。

)It’s about three years since I last played basketball. 我差不多有三年没有打篮球了。

(直译：自从我上次打篮球以来已差不多有三年了。

)请看有关高考题(答案为DDBCDC)：1. That was really a splendid evening. It’s years _________ I enjoyed myself so much. (安徽卷)A. whenB. thatC. beforeD. since2. It was some time _________we realized the truth. (山东卷)A. whenB. untilC. sinceD. before3.—Did Jack come back early last night?—Yes. It was not yet eight o’clock _________he arrived home. (福建卷)A. beforeB. whenC. thatD. until4. Scientists say it may be five or six years _________it is possible to test this medicine on human patients. (福建卷)A. sinceB. afterC. beforeD. when5. It was evening we reached the little town of Winchester. (天津卷)A. thatB. untilC. sinceD.before6. It _________ long before we _________ the result of the experiment. (上海春)A. will not be; will knowB. is; will knowC. will not be; knowD. is; know【全真模拟训练】1. It was about midnight _________ we found the lost child, crying under a tree.A. thatB. untilC. whenD. where2. It's some time _________ I have spoken to you about this matter.A. thatB. unlessC. sinceD. until3. It was ten _________ he stood at aunt’s door and rang the bell.A. whenB. untilC. sinceD. that4. I think it won’t be long _________ they understand each other.A. whenB. untilC. sinceD. before5. How pleased I am tonight! It’s years _________ we had so great a time together.A. whenB. thatC. beforeD. since6. It was some time _________ we realized how important the matter is.A. whenB. untilC. sinceD. before7.—Did you come home very late last night?—No. It was just half past seven _________ I appeared before my parents.A. thatB. whenC. untilD. since8. How time files! It seems like years _________ I last saw you.A. whenB. thatC. sinceD. before9. It’s more than half a century _________ the People’s Republic of China was liberated.A. whenB. thatC. sinceD. after答案：1—5 CCADD 6—9 DBCCwhen〔引导时间状语从句〕具体地说，它有以下几种含义：1．表明一个动作发生的时候，另一个动作正在进行之中。

It+be+时间+before/since/when/that句型辨析I since1。

翻译“It is/has been+时间段+since从句”(1)当从句谓语动词为非延续性动词时，表示这段时间从该动作开始时算起，即“自从做……以来已经多久了".（2）当从句谓语动词为延续性动词时，表示这段时间从动作结束时算起，即“自从不做……以来已经多久了”。

It is two years since he joined the army.他参军两年了。

（从参军那一刻算起)It is two years since he was a soldier。

他退役两年了。

(从他不再是士兵算起)2. 时态主句为现在时（一般或完成），从句都是一般过去时.主句为过去式（一般性都用was就够了），从句都是过去完成时II before1. 翻译It was/will be+时间段+before.。

.过多长时间将发生某动作或事情;或过了多久发生了某事或动作.It was three years before he finished the work.他花了三年才完成这项工作。

It will be three years before he finishes the work。

他得花三年才能完成这项工作。

2。

It won’t be/take long before...不久就会…It won’t be long before he finishes the work.他不久就会完成这项工作。

2。

时态主句为过去式（一般性都用was就够了)，从句用过去时主句为将来时,从句用现在时（用一般现在时表示将来）III when1. 翻译It is + 时间点+ when…当发生什么的时候是什么时候…It was one o’clock when he came in 。

2. 时态主句是什么时态，从句就是什么时态3。

常考与强调句的区别It was five o'clock when we arrived at the small mountain village。

It+be+时间+before/since/when/that句型辨析I. since1.It is/has been+时间段+since sb did sth某个动作发生持续多久eg:It is/has been three years since he finished the work.自从他完成这项工作已经三年了.2.该句型中若since后跟延续性动词，要翻译成否定含义,即“没做某事已经多久了”.eg:It has been three years since he worked here.他不在这工作已经三年了.It has been three years since he smoked.他已经戒烟三年了.但是：It has been three years since he began to smoke.他吸烟有三年了。

II.before.1.It was/will be+时间段+before... 过多长时间将发生某动作或事情；或过了多久发生了某事或动作。

eg:It was three years before he finished the work.他花了三年才完成这项工作.It will be three years before he finishes the work.他得花三年才能完成这项工作.2.It won't be/take long before...不久就会…eg:It won't be long before he finishes the work.他不久就会完成这项工作.III when.when没有固定与It is…连用的句型.when可表示时间点或时间段，因此从句中短暂性动词或延续性动词均可用.when还可作并列连词，表示突然发生一个动作,等于and at that time.常用句型:1主语+was/were doing when...2主语+was/were about to do when...It+be+时间+before/since/when/that重要考点练习It +be+时间+before/since/when/that…是高考中每年必考的重要考点，而学生却对这个句型中几个关联词的选择把握不准，造成失分。

It …+点时间/段时间+before…诠释高中英语中，before句式，相似性强，考生易混淆，究其用法，现小结于后，敬供商榷。

1. It was / will be + 段时间+ before …在“It was / will be + 段时间 + before 从句”结构中，before是从属连词，表示“……才；……就”，引导时间状语从句。

例：It was just 3 days before the book was published.三天后那本书就出版了。

例：It will be five years before we meet again.五年后我们才会在见面。

2. It wasn’t long before …/ It won’t long before …在“It wasn’t long before从句”结构中，before是从属连词，表示“不久以后就……”；而“It won’t long before从句”结构中，before是从属连词，意为“不久就会……”，引导时间状语从句。

例：It wasn’t long before he came home.他不久后才（很快）回到了家里。

例：It won’t long before you get well again.不久你就可以恢复健康了。

3. It be + 点时间+ before …在“It be +点时间 + before从句”结构中，before是从属连词，表示“在……之前；时间是……”，引导时间状语从句。

例：It was 4:00 before he came to see you.他是四点后来看你的。

4. It be + 点时间+ when …在“It be +点时间 + when从句”结构中，when是从属连词，表示“当时是……”，引导时间状语从句。

例：It was 4:00 when he came to see you.他来看你时，已是四点了。

例3：It‘s high time we took measures to solve this problem
1.It is/has been + 时间段 + since + 一般过去时
例1：It is/has been 10 years since he came here.
It was+时间段+since(从句用过去完成时) 例2：It was years since he had arrived in China.(过去时+since+过去 完成时)
例2：It will be midday when they get home.当他们到家时将是中午。
4. It/This is + the + 序数词 + 时间 +（that）定语从句(从句用现在完成时)
例1：It is the first time (that) I have been here.
It wasn’t 3 years before we met again. (没过3年我们就又见面了) It will be two years before we meet again. (还要过两年我们才能见面) It won’t be long before you regret. （用不了多久你就会后悔） We didn’t wait long before he came back. (我们没等多久他就回来了)
例1：It is (high) time (that) we stopped pollution.
其中that引导的从句中也可用should +V(原形), should不可省。
例2：It is (high) time (that) you came/should come here.