第2个回答 2011-02-27
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
介词 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。
连接词 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常见的四种用法
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 been here.
4) It is +一段时间+ since从句
It is two years since I became a postgraduate student.
若since引导的状语从句的谓语动词是终止性动词的过去时，则从句表示的时间是“从动作开始的那一时刻起”， 这是最常见的一种用法。如：
He has studied very hard since he came to our school.
自从他来到我们学校，学习就非常努力。
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，则从句表示的时间是“从那个持续动作或状态结束时算起”。如：
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。”这种句型常被人们误解，我们再多举几个例子看看：
It is half a month since he was a League member.
他退团半个月了。
It”s been quite some time since I was 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，他经常给我写信。
（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，他就经常给我写信。
（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。
自从他住在那儿起，我就一直没收到他的来信。
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。
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： 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。
由此可见，since引导的从句中，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。
It is + 一段时间 + since ... 这个句型与It has been + 一段时间 + since ... 意思相同。如：
It is ten years / It has been ten years since they last met.
自从他们上次碰面之后已经10年过去了。