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since和 after的差异 since后面接的是某一时间点,表示从过去某一点时间延续到现在或过去,主句谓语动词要用完成时态,但当句子主语是 it时,也可用一般现在时｡ after作介词或连词可以表示时间,同过去时或将来时连用,但不能和现在时间发生关系,不能同现在完成时连用｡例如: After her graduation, she has worked in the factory. (误) Since her graduation, she has worked in the factory. (正) After her graduation, she worked (will work) in the factory. (正) She is without a boyfriend since leaving home. (since 1988）. (误) She has been without a boyfriend since leaving home. (正) I have never been there since two years. (误, two years为一段时间 ) I have never been there for two years. (正) It is (has been) five weeks since he started on the journey. (正) He has served as manager of the company since four years ago. (正) |
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