在大学英语六级考试中，单独考察六级语法的题型不多，但是语法知识点却贯穿整张试卷，下面是新东方在线英语六级频道为大家整理的大学英语六级基础语法知识：since的四种用法，希望可以为大家带来帮助。

　　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.

　　2016年12月大学英语六级基础语法知识汇总