高考问答商品房备案需要多久:烦请告诉在什麼情况下用"SINCE",它的主要用法是什麼???
来源：百度文库 编辑：高考问答 时间：2024/04/30 02:44:14
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)。
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
1.可以用于点时间前，用在现在完成时态：
I have been here since last year.
2.用于原因，意思是既然
Since every one is here,let's begin our class.
介词 自～以来
连词 自从，既然
主句（完成时）＋SINCE＋时间从句(过去时)
SINCE+原因从句+主句
SINCE+条件从句+主句