since等的辨析

Since\before\until的辨析
练习：the soldier devoted most of his time to the security of the country. and it has been three years ____he went home .A. before B. after C. since D until
,It has been two years___ I graduated from my high school.
自从我高中毕业,已经两年了.
It is still a year ___ I graduate from my college.
在我大学毕业之前,仍然还有一年的时间.
I had finished my homework ____ it was 9 o`clock last night. 在昨天晚上9点之前,我就已经完成了我的作业.
I did not finish drawing the picture ____ it was 9 o`clock last night. 直到昨天晚上9点我才画完这幅画.
since是自从的意思”一段时间+since”表示从这个时间开始到现在---自从~以来. 用法上It + ( 现在完成时) + 一段时间+ since + ( 一般过去时)例句：It is / has been four days since I caught a cold.我感冒已四天了It is / has been two weeks since we met last.自从我们上次见面以来已过了两周.
一段时间+ before表示在这个时间之前,或者大约在这个时间上就会发生某事.用法上It + ( 一般将来时) + 一段时间+ before +( 一般现在时)例句：It will be five years before he meets you again. 五年之后他就会再见你的. It + be (not) + long before表示"(不)很久/ 才…"或"(没)过多久就/ …"It was (not) long before ….(谈论过去)\ It will
(not) be long before ….(谈论将来)\ It was long before she came back.\没过多久她就回来了.\ It will be long before we meet again.\x0d很久以后我们才会再见面.\ It will not be long before we turn our hope into reality. 过不了多久我们的希望就会变成现实. 这里it指时间, before是连词,引导时间状语从句.long可用一段时间来替代.
Until
1. 如果（主）句中的谓语动词是终止性动词即非延续性动词,应采用
“...not ...until ...”结构,意为“……到……时候才……”.例如：
You mustn’t eat anything until you see the doctor.
看过医生之后,你才能吃东西.
Don’t get off the bus until it has stopped. 车停稳了以后再下车.
2. 用于肯定句中：
1) It may last until Friday.这可能要延续到星期五.
2) He will be working until 5 o'clock.他将一直工作到五点钟.
3) She was a bank clerk until the war, when she trained as a
nurse.她战前是个银行职员,战时受训当了护士.
不难看出until 用于肯定句中,表示句子的动作一直持续到until短语所表示的时间为止,即表示动作的终点.一般可译为“直到……时(为止)”或“在……以前”.在这种用法中,句子的谓语动词必须是持续动词(非瞬间动词),如live, wait ,last, love, like, stay, work, continue等.
3. 如果谓语动词为否定式,则until应译为“到……时候才”,即“在……
以前不”.例如：
I did not watch TV until she came back.（= I began to watch TV
when/after she came back.）
直到她回来我才开始看电视.
4. 连词until引导的从句中谓语动词的时态.
1）主句的谓语动词为一般现在时或一般将来时时,until从句中的谓语动词为现在完成时,用来强调从句谓语动词表示的动作发生在主句谓语动词表示的动作之前.试比较：
I won’t go to bed until I have finis hed my homework.
我要完成作业才睡觉.
2）主句中的谓语动词为一般过去时时,从句中的谓语动词为过去完成时,用来强调从句谓语动词的动作发生在主句谓语动词表示的动作之前.试比较：
Li Lei didn’t come until the film had begun.
直到电影开演,李雷才来.
〔特别提醒〕till和until的意思基本相同,用法也基本一样,但until 语气较重,多用于较正式的文体里.till多用于英式英语,until多用于美式英语；till不能用在句首,也不能用在not开头的短语或从句里,而until可以.例如：
Until he came home, we knew the news.
在他到家之前,我们不知道这消息.
Not until nine o’clock yesterday evening did we finish the work. until和before用法的区别
一、在下列情况下,两者可互换用,但含义略有不同.before表示“在……之前”的意思,强调时间先后关系；而until表示“直到……才”的意思,主句是肯定句则表示主句动作的终止时间；主句是否定句则强调主句动作的起始时间.
1.主句为否定式终止性谓语动词.常见的动词是open, start, leave, arrive, finish, stop等.例如：
(1)The noise of the street didn't stop until/before it was midnight.
(2)The children won't come back until/before it is dark.
(3)I didn't leave the lovely boy until/before his mother came home.
2.主句为肯定式、延续性谓语词,这类动词用stand, stay, talk ,be, wait 等.例如：
(1)He lived with his parents until/before he graduated from school.
(2)I will wait until/before he comes to my help.
(3)I shall stay here until/before you come back.
二、在下列情况下,用before不用until.
1.主句这肯定式、终止性谓语动词,只用before.“在…之前就”、“没来的及就”
(1)He fell asleep before I could take off his clothes.
(2)We arrived there before it started to rain.
(3)The holiday came to the end before I knew it.
(4)He almost knocked me down before he saw me.
2.主句谓语动词强调动词的迟缓性,只用before,常伴有时间段状语或时间段暗示.例：
(1)It was quite some time before he found the elephant at all.
(2)We had walked a long way before we found some water.
(3)We had sailed for two days before we saw the land.
(4)The fire lasted about four hours before the firefighters could control it.
(5)It was midnight before my brother came home.
(6)It was three months before they met again.
3.如果强调从句谓语动作未发生,就发生主句谓语动作,只用before.常译为“未及”,“不”或“不等……就”.例：
(1)We can leave early in the morning before it gets too hot.
(2)I must write it down before I forget it.
(3)We do want to buy something now before prices go up.
4.在某些特定句型中用before.例如：
(1)It was not long before the whole country rose up.
(2)It will probably not be long before they understand each other.
三、下列情况一般区别用until.
1.主句是持续性谓语动词时,肯定、否定都可以,但意义完全不同.肯定表动作终止,而否定表动作开始.例如：
(1)We discussed the problem until/before he came back.我们一直
讨论到他回
来.
(2)We didn't discuss the problem until he came back.我们一直等到他回来后才讨论问题.
2.not…until句型尽管在某些情况下可与before互换用,但在强调句中一般仍用until.
例如：
(1)It was not until he told me that I knew it.
(2)It was not until he finished his homework that he went home.。