since+什么时?

since
表示从什么时候开始
例子 since 2004
是指 2004到现在
for
是指一段时间
例子 for 2004 to 2006
指的是04年到06年
SINCE后面加时间点
例如 SINCE 1990 意思就是从1990开始
1990就是一个时间点；
而FOR后面是加时间段
例如 FOR 5 YEARS
意思就是5年的时间
since+过去某一时间或句子,for+一段时间
She has taught in the school for ten years. 她在这所学校教书已经10年了.
I haven't eaten anything since breakfast. 我从早饭起就一直没有吃东西.

介词

since的用法
1)since +过去一个时间点　(如具体的年、月、日期、钟点、1980,last month,half past six).
I have been here since 1989.
2)since +一段时间+ ago
I have been here since five months ago.
3)since +从句　
Great changes have taken place since you left.
Considerable time has elapsed since we have beenhere.
4) Itis +一段时间+ since从句
It is two years since I became a postgraduatestudent.
since的用法主要有两点：一是表示“自从……以来”,二是表示“既然”之意.但如果只了解词的含义,而不了解其用法,在使用时就会造成错误.例如：Ihave not heard from him since I lived in Shanghai.
不少人会望文生义,将该句译为：“自从我住在上海以来,就再也没有收到他的信了.”而实际上这个句子的译文并非如此,那么正确的含义是什么呢?
下面谈谈since作连词引导时间状语从句的用法.
一、若since引导的状语从句的谓语动词是终止性的过去时,则从句表示的时间是“从动作开始的那一时刻起”.如：
He has studied very hard since he came to ourschool.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.
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持续性动词或表示状态的动词的过去时时,则从句表示的时间是“从那持续动作或状态结束时算起”.如：
I haven’t heard any noise since I slept.Sleep 为持续性动词,sleep的动作结束时,即“醒来”时,这句应译为“我醒后还未听到任何声音”.
John is now with his parents in New York,it isalready 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.
本文开始出现的那个句子就可以译为“自从我离开上海,就再也没有收到他的信.”这种译法常被人们误用,我们不妨再多举几个例子看看：
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.他离开团队（不当团队成员）半个月了.
It’s beenquite some time since I was last in London我离开伦敦已很长时间了.
比较：He has written to me frequently since I wasill.自从我病愈以来,他屡次给我写信.（从句谓语为状态动词）
He has written to me frequently since I fell ill.自从我生病以来,他就屡次给我写信.（从句谓语为终止性动词）
三、若since引导的状语从句的谓语为持续性动词的现在完成时,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：
I haven’t heard from him since he has lived there.
这里has lived表示动作的持续性,时间的起点应从：“开始居住”时算起.因此此句可理解为“自从他（开始）住在那儿起,我就一直没收到他的来信”.
Since we have owned a car,we have gone campingevery year.自从我们自己有了汽车,我们每年都去野营.
试比较：1.Since I’ve been at this school,we have had threeheadmasters.自从我到这所学校,我们已换了三个校长了.
Since I was at this school,they have had threeheadmasters.自从我离开这所学校,他们已换了三个校长了.
2.He has never been to see me since I have beenill.自从我生病以来,他从未来看过我.
He has never been to see me since I was ill.自从我病愈以来,他从未来看过我.
由此可见,since引导的从句持续动词的一般过去时和现在完成时所表示的意思恰好相反.换言之,前者以肯定的语法形式反映着否定的逻辑内容,而后者的形式与内容是一致的.
至于It is +一段时间+since…的句型与It has been +一段时间+since…意思相同.前者是规范说法,后者是口语说法.
应注意的是,在这种结构中,since引导的从句绝对不能用否定式的谓语动词来表示否定意义,下面两句都错了：
It is a long time since he didn’t study English.
It’s twomonths since you didn’t come tosee me.
正确的说法为：
It’s a longtime since he studied English 他好久没学英语了.
You haven’t come to see me for two months.你有两个月没来看我了.

It is +一段时间+since...意思是“自.发生以来已经一段时间了”.
如：
it is three years since he died.(自)他去世以来已经三年了.
It is +一段时间+before...意思是“过了一段时间...才发生”
如：
It is 3 years before they accept the fact.过了三年他们才接受这个事实.

since+时间点,for+时间段
前者表示从某个时间点开始一直到现在过程做的事或者持续的事
后者表示一段时间内做的事或者持续的事

他们都跟现在完成时态连用,表示时间的持续
可以互换
since two years 是错误的

具体的一段时间 比如说a few years 、2days 就用for
点时间就是从过去的某个时间点开始的,比如说 yesterday、2011、2 days ago~

starts,固定用法,since前用完成时,since后用一般现在时.谢谢,希望采用~

英语中表示时间段的方法很多.如果是for的话 举个例子 I’ve studied English for ten years.（我已经学习英语十年了）这个就是时间段
since的话 I'v study English since I was ten years old.（我从十岁开始学习英语）
虽然都表达了学习英语时间的长短 但是用的词不一样是段是点就不一样
这样会稍微清楚点么.貌似我说得也不太清楚

1. (1) My brother has been in the army for two years. (2) My brother has been in the army since 2008. (3) My brother has been in the army since two years ago. (4) It's two years since my brother jioned the army. --- jion 是终止性动词,不能与延续时间连用.即不能用于 （1）,（2）,（3）句中. 2. (1) I have kept this dictionary for ten days. (2) I have kept this dictionary since September 1st. (3) I have kept this dictionary since ten days ago. (4) It's ten days since I borrowed this dictionary. --- borrow 也是终止性动词,与延续性时间连用时,要转换成 keep

since是自从的意思,表示从一个过去确定的时间点到现在一直保持着这个状态,并且有可能持续下去,用present perfect
从我出生起我一直住在这里：I've lived here since I was born

不可以
have been in 可以加
He has been in China for 2 years/ since 2 years ago.

since一般不跟现在一般时态
since常跟过去一般时态,主句用现在完成时态
it has been 3 years since I left my hometown.
since是指从说话前某一时刻到说话时这一段,所以since后一般要用过去一般时态

1.自从【过去时间点】以来2.自从【时段】前以来3.自从【从句内容】以来4.自从【since后面的内容】已经有【时段】了.满意的话别忘了采纳哦~谢谢.

+从句用过去时,它的主句现在完成.
It has been three years since I came here.
自从我来到这 已经三年了.

视情况而定.it has been a long time since a serious war occurred in the western world.
it has been a long time since the technology has motivated us to make things.
谓语为过去式的多表示已经过去的,为过去分词的多表示还在持续进行的对现在还是如此的状态.一般中学考试多考虑为第一种.

efore也有类似句型,但是主从句时态和since不同.
since为：It is + 一段时间 + since从句（一般过去时）
或：It has been + 一段时间 + since从句（一般过去时）
或：It was + 一段时间 + since从句（过去完成时）
意思是：自从...以来已经多久了.
而before为：It took/was + 一段时间/long + before从句（一般过去时）意思是：过了多久才...
否定为：It wasn't 或 didn't take + 一段时间/long + before从句（一般过去时） 意思是：没过多久就...
或者：It will be/take + 一段时间/long + before从句（一般现在时）意思是：要过多久才会...
否定为：It won't be/take + 一段时间/long + before从句（一般现在时）意思是：不用过多久就会...

一般情况下是的.但有时since表示既然/由于,不用完成时.如“I must calm down since I was still alive”（我必须冷静下来,既然我还活着）
my sister has bought in the shop already这句话是对的.我是初二的学生,虽然我不知道初三时现在完成时是怎样的,但在初二的完成时中,只有含since和for的句子才需改用延续性动词.

都用完成时,完成时包括许多
since
adv.(常用于现在完成时或过去完成时)
1.此后;从那时到现在
She left school three years ago and has worked as a nurse ever since.
她三年前毕业,从那时起便一直当护士.
2.之前,以前
prep.
1.(常用于现在完成时或过去完成时)自...以来,从...至今
I haven't heard from him since last year.
我自去年以来未曾收到过他的信.
conj.
1.(常用于现在完成时或过去完成时)自...以来,从...至今
It's been ten years since they married.
他们结婚到现在已经十年了.
She has been living a hard life since her husband died.
她自从丈夫死后,一直过着艰苦的生活.
2.既然;因为,由于
He must have taken the book since it isn't here.
他一定是把书拿走了,因为书已不在这里了.
Since it is so hot,let's go swimming.
既然天气这么热,我们去游泳吧.
since的用法主要有两点：一是表示“自从……以来”,二是表示“既然”之意.但如果只了解词的含义,而不了解其用法,在使用时就会造成错误.例如：I have not heard from him since I lived in Shanghai.
不少人会望文生义,将该句译为：“自从我住在上海以来,就再也没有收到他的信了.”而实际上这个句子的译文并非如此,那么正确的含义是什么呢?
下面谈谈since作连词引导时间状语从句的用法.
一、若since引导的状语从句的谓语动词是终止性的过去时,则从句表示的时间是“从动作开始的那一时刻起”.如：
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.
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持续性动词或表示状态的动词的过去时时,则从句表示的时间是“从那持续动作或状态结束时算起”.如：
I haven’t heard any noise since I slept.Sleep 为持续性动词,sleep的动作结束时,即“醒来”时,这句应译为“我醒后还未听到任何声音”.
John is now with his parents in New York,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.
本文开始出现的那个句子就可以译为“自从我离开上海,就再也没有收到他的信.”这种译法常被人们误用,我们不妨再多举几个例子看看：
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.他离开团队（不当团队成员）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.
比较：He has written to me frequently since I was ill.自从我病愈以来,他屡次给我写信.（从句谓语为状态动词）
He has written to me frequently since I fell ill.自从我生病以来,他就屡次给我写信.（从句谓语为终止性动词）
三、若since引导的状语从句的谓语为持续性动词的现在完成时,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：
I haven’t heard from him since he has lived there.
这里has lived表示动作的持续性,时间的起点应从：“开始居住”时算起.因此此句可理解为“自从他（开始）住在那儿起,我就一直没收到他的来信”.
Since we have owned a car,we have gone camping every year.自从我们自己有了汽车,我们每年都去野营.
试比较：1.Since I’ve been at this school,we have had three headmasters.自从我到这所学校,我们已换了三个校长了.
Since I was at this school,they have had three headmasters.自从我离开这所学校,他们已换了三个校长了.
2.He has never been to see me since I have been ill.自从我生病以来,他从未来看过我.
He has never been to see me since I was ill.自从我病愈以来,他从未来看过我.
由此可见,since引导的从句持续动词的一般过去时和现在完成时所表示的意思恰好相反.换言之,前者以肯定的语法形式反映着否定的逻辑内容,而后者的形式与内容是一致的.
至于It's+一段时间+since…的句型与It has been +一段时间+since…意思相同.前者是口语说法,后者是规范说法.

完成时 +since+过去式
`(*∩_∩*)′

three days就是段,three days ago就是点.你可以这么理解,for后面是接一段时间,例如从星期一到星期四.since接点时间,例如星期一这天.