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。