since的4种时态用法

动词的时态：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。