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.
英语六级语法知识:现在进行时代替将来时
1) 表示即将发生的或预定中计划好的活动。
Are you staying with us this weekend? 这周和我们一起度周末吗?
We are leaving soon. 我们马上就走。
2) 渐变动词,如:get, run, grow, become, begin及die。
He is dying.