for与since 的辨析_学习方法网
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for;since
for与since都能与现在完成时连用,但区别较大:
for后须接“时间段”,since后须接“时间点”,二者可以转换,均须与延续性动词连用,也可以与非延续性动词的
否认式连用。二者引出的时间状语往往用 how long提问。如:
He has been here for two years.=He has been here since two years ago.他来这里已有两年了。
—How long have you had this book?这本书你买多久了?
—For a week./Since a week ago.买一周了。
We haven't heard from him for a month.我们已有一个月没收到他的来信了。
since能引导时间状语从句
〔主句用现在完成时,从句用一般过去时
〕,而for
那么不 ...


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