1.现在完成时由“have(has)+过去分词”构成，第三人称单数用has，其他情况下都用have:
He (She, The boy) has gone home
他(她，那男孩)回家了。
I (You, We, They) have made a mistake.
我(你，我们，他们)犯了一个错误。
2.和过去式一样，过去分词也有两类，规则动词)加-ed构成，不规则动词有各自不同的形式，如do一done, find—found, see—seen, hear—heard。
3.现在完成时主要表示：
1)已发生且对现在有影响的动作：
Who has broken the glass?
谁把玻璃杯打破了?(杯子破了)
I haven't had my breakfast yet.
我还没吃早饭。(有些饿)
He's already left for the airport.
他已动身去机场。(不在家)
2)现在以前这段时间发生的情况：
She's just phoned.
她刚打电话来。
There has been an accident.
出了车祸了。
They have put up hundreds of tall buildings.
他们盖了数以百计的高楼。
3)持续到现在的状态：
She has been here for two years.
她在这里已经有两年了。
The meeting has already lasted for 3 hours.
会已经开了三个小时了。
We have lived here for over ten years.
我们在这里住了十多年了。
若有表示过去时间的状语则不能使用这个时态。另外have (has)got+有特殊意义，表示“有”：
How many brothers have you got?
你有多少兄弟?
He hasn't got a car.
他没有汽车。
现在完成时的肯定、否定、疑问及简易回答形式可表示如下：
1.肯定句
I(We, You, They)have done it.
2.否定句
I(We, You, They)haven't done it.
He (She) has left.
He(She) hasn't left.
I (We, You, They) haven't.
3.疑问句
Has he (she) left?
Have I (We, You, They) have done it?
4.简短回答
Yes, he (she) has.
he (she) hasn't.
No, I (We, You, They) haven't.
