必备语法：比较过去时与现在完成时

　　1)过去时表示过去某时发生的动作或单纯叙述过去的事情，强调动作;现在完成时为过去发生的，强调

　　过去的事情对现在的影响，强调的是影响。

　　2)过去时常与具体的时间状语连用，而现在完成时通常与模糊的时间状语连用，或无时间状语。

　　一般过去时的时间状语:

　　yesterday, last week，…ago, in1980, in October, just now, 具体的时间状语

　　共同的时间状语:

　　this morning, tonight,this April, now, once，before, already, recently，lately

　　现在完成时的时间状语

　　for, since, so far, ever, never, just, yet, till / until, up to now, in past years,

　　always,

　　不确定的时间状语

　　3)现在完成时可表示持续到现在的动作或状态，动词一般是延续性的，如live, teach, learn,

　　work, study, know.

　　过去时常用的非持续性动词有come, go, leave, start, die, finish, become, get married等。

　　举例：

　　I saw this film yesterday.

　　I have seen this film.

　　Why did you get up so early?

　　Who hasnt handed in his paper?

　　She has returned from Paris.

　　她已从巴黎回来了。

　　She returned yesterday.

　　她是昨天回来了。

　　He has been in the League for three years.

　　He has been a League member for three years.

　　He joined the League three years ago.

　　I have finished my homework now.

　　---Will somebody go and get Dr. White?

　　---Hes already been sent for.

　　句子中如有过去时的时间副词时，不能使用现在完成时，要用过去时。

　　Tom has written a letter to his parents last night.

　　Tom wrote a letter to his parents last night.

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