2个回答
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。
副词 ad. (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
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。