Question

since的用法是什么？

Answer 1

回答如下：
英语since可以作从属连词，引导时间和原因状语从句。它还可以作介词和副词。例如：
Since we parted, we haven't seen her. 自从我们分手后，我们就一直没见过她。(时间状语从句，从句要用一般过去时，主句用现在完成时)
Since last year I have been at home. 从去年以来，我一直呆在家。(介词，主句要用现在完成时)
We had better give up smoking since it is harmful to our health. 我们最好戒烟，因为它有害于健康。
He came to Nanjing 6 years ago and has lived here (ever) since.他6年前来到南京，从此便住在这里。(副词，主句用现在完成时。)

Answer 2

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。