文档介绍：时态讲解：现在完成时
构成：现在完成时由助动词have+过去分词构成，助动词have有人称和数的变化。第三人称单数用has，其余用have。
现在完成时的否定式、疑问式和简单回答形式如下：
否定式
疑问式
I have not(haven’t) studied…
Have I studied…?
You haven’t studied…
Have you studied…?
He hasn’t(has not) studied…
Has he studied…?
否定疑问句
简单回答（肯定/否定）
Have I not (Haven’t I) studied…?
Yes, you have. No, you haven’t.
Have you not( Haven’t you) studied…?
Yes, I have. No, I haven’t.
Has he not (Hasn’t he) studied…?
Yes, he has. No, he hasn’t.
用法：
现在完成时通常表示在说话之前已经完成的动作或存在的状态。说话人强调的是该动作或状态对现在的结果或影响。如：
My daughter has just gone out. 我女儿刚出去。
I’m sure we’ve met before. 我肯定我们以前见过面。
She has arrived. 她到了。
表示持续到现在的动作或状态，往往和包括现在在内的表示一段时间的状语连用，如recently, already, just, lately, for…, since… yet等，如：
I haven’t heard from her these days. 这些日子我没有收到她的信。
We haven’t seen you recently. 最近我们没有见到你。
They have been away for two years. 他们离开已经两年了。
注意★：
I ）since 和 for的区别
since 后接时间点，如1993， last term, yesterday, the time I got there
for 后接一段时间，表示“长达多久”，如ten years, a while, two days 等。
Excersice：用since 和 for 填空
1， Jim has been in Ireland Monday.
2， Jill has been in Ireland three days.
3， His aunt has lived in Australia 15 years.
4， Mary has been in her office 7 o’clock.
5， India has been an independent country 1974.
6， The bus is late. They have been waiting 20 minutes.
7， Nobody lives in those houses. They have