现在完成时

　　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。

　　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：我昨天看了这部电影

　　(强调看的动作发生过了。)

　　I have seen this film：我已经看过这部电影

　　(强调对现在的影响，电影的内容已经知道了。)

　　Why did you get up so early

　　(强调起床的动作已发生过了。)

　　Who hasn't handed in his paper

　　(强调有卷子，可能为不公平竞争。)

　　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：他在团中已经三年

　　(在团内的状态可延续)

　　He has been a League member for three years：他连续三年被一个团内的成员

　　(是团员的状态可持续)

　　He joined the League three years ago：他三年前入团

　　( 三年前入团，joined为短暂行为。)

　　I have finished my homework now.

　　---Will somebody go and get Dr. White

　　---He's already been sent for.

　　句子中如有过去时的时间副词(如 yes terday,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.

　　用于现在完成时的句型

　　1)It is the first / second time…. that…结构中的从句部分，用现在完成时。

　　It is the first time that I have visited the city.

　　It was the third time that the boy had been late.

　　2)This is the… that…结构，that 从句要用现在完成时.

　　This is the best film that I've (ever) seen.

　　这是我看过的最好的电影。

　　This is the first time (that) I've heard him sing.　这是我第一次听他唱歌。

　　典型例题

　　(1) ---Do you know our town at all?

　　---No,this is the first time I ___ here.

　　A. was　B. have been　C. came　D. am coming

　　答案B. This is the first time 后面所加从句应为现在完成时，故选B。

　　(2) ---Have you ____ been to our town before

　　---No,it's the first time I ___ here.

　　A. even,come　B. even,have come　C. ever,come　D. ever,have come

　　答案D. ever意为曾经或无论何时，反意词为never，此两词常用于完成时。This is the largest fish I have ever seen. It is / was the first time +that-clause 的句型中，从句要用完成时。

　　注意：非延续性动词的否定形式可以与表示延续时间的状语连用。即动作不发生的状态是可以持续的。

　　(错)I have received his letter for a month.

　　(对)I haven't received his letter for almost a month.