零基础英语学习：since的四种用法

　　零基础英语学习1) since +从前一个时间点　(如具体的年、月、日期、钟点、1980, last month, half past six)。 内容来自

　　I have been here since 1989. 内容来自

　　2) 零基础英语学习since +一段时间+ ago

　　I have been here since five months ago.

　　3) 零基础英语学习since +从句

　　Great changes have taken place since you left.

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　　Considerable time has elapsed since we have been here.

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　　4) 零基础英语学习It is +一段时光+ since从句

　　It is two years since I became a postgraduate student.

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