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since 的种时态用法 Prepared on 22 November 2020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，lastmonth，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。