2015年卫生职称英语语法：since的四种用法
2014-09-05 09:23 来源：医学教育网
2015年职称英语考试已经开始备考，本阶段应该多整理一些基础词汇和语法。为此，网校特整理了“2015年职称英语考试语法知识”供您参考，希望对您有帮助！
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.
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