4. 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，其结果对现在造成影响。

（1）过去发生的动作发生到现在，刚刚完成；

（2）从过去发生的动作，发生到现在，刚刚告一段落，但是后面会继续发生； eg：I have just finished my homework.

It has rained for 3 days.

过去时与现在完成时的区别：

（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。

eg：I came to Beijing in 1995.

I have stayed in Beijing since 1995.

（2）过去时常与具体的时间状语连用，而现在完成时通常与段的时间状语连用，或无时间状语；

一般过去时常用时间状语：yesterday, last week，…ago, in1980, in October…（具体时间）

现在完成时常用时间状语：for, since, so far…（长期的段时间）

eg：He had dinner with me yesterday.

I have played basketball for 3 hours.

（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；

eg：He got married two years ago.

I have lived in Beijing for 10 years.

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

---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。

since和for的用法：

since 用来说明动作起始时间，for用来说明动作延续时间长度;

eg：I have lived here for more than twenty years.

I have lived here since I was born.

for后面多接一段时间，而since后面则接一个时间点，若since后面也出现时间段，则在时间段后加ago；

eg： I have lived here sincetwenty years ago.

错句：I have worked here since many years.

since句型：

It is +一段时间+ since从句，since从句要用一般过去时；

eg：It is two years since I became a postgraduate student.

It is three years since I joined the army.