since 在时,有几种可能的时态,分别是什么

since 在时,有几种可能的时态,分别是什么
since 在时,有几种可能的时态,分别是什么

since 在时,有几种可能的时态,分别是什么
since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）.例如：
I have been here since 1989.1989起,我一直在这儿.
2） since +一段时间+ ago.例如：
I have been here since five months ago.我在这儿,已经有五个月了.
3） since +从句.例如：
Great changes have taken place since you left.你走后,变化可大了.
Great changes have taken place since we were here.我们走后,变化可大了.
4） It is +一段时间+ since从句.例如：
It is two years since I became a postgraduate student.我考上研究生有两年了.
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.
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”.

现在完成时，一般过去时