英语现在完成时

很急的

现在完成时用来表示之前已发生或完成的动作或状态，其结果的确和现在有联系。动作或状态发生在过去，但它的影响现在还存在；也可表示持续到现在的动作或状态。其构成：have(has)+过去分词。现在完成时通常与模糊的时间状语连用，或无时间状语。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等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.(强调看的动作发生过了。) I have seen this film.(强调对现在的影响，电影的内容已经知道了。) 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.（在团内的状态可延续） He has been a League member for three years.(是团员的状态可持续) He joined the League three years ago.(三年前入团，joined 为短暂行为。) I have finished my homework now. ---Will somebody go and get Dr. While? ---He's already been sent for.句子中如有过去时的时间副词（如yesterday,last,week,in 1960）时，不能使用现在完成时，要用过去时。（错）Tom has written a letter to his parents last night.(对)Tom wrote a letter to his parents last night.