现在完成时、过去完成时和被动语态

I. The Present and Past Perfect Tense II. The Passive

现在完成时主要表示：（1）动作或过程发生在说话之前某个时刻，到现在已经完成，

兵语现在的情况有联系；常和一些表示不确定时间的副词连用。如：already ,ever ,

just, never, often ,yet等。Have you ever travelled by air ?你乘过飞机旅行吗？

We have already learnt a lot of English knowledge.我们已经学了很多英语知识。

（2）动作或状态从过去某一时刻开始，持续到现在刚刚结束，或可能在继续下去；

常和for since等词连用。如：

He has stayed under water for seven days.他已经在水下呆七天了。

He has learnt a lot since he came here.他到这以来已经学了不少东西。

注：现在完成式和一般过去时的动作都发生在过去某一时刻。现在完成时从“现在”看问题，强调动做与现在的联系，所以通常不和表示过去某一确定时间的状语连用;

而一般过去时则从“过去”看问题，说明动作在过去某一特定时刻发生，不涉及语现在的

或完成。常和介词by（意为“在…之前”，如：by four o’clock ,by that time ,by the end of last week 等），before以及表示过去时间的状语从句连用。如：

By nine o’clock last night ,we had got 200 pictures from the spaceship .到昨晚九点钟之前为止，我们已经从那艘宇宙飞船收到了二百张照片。

The play had already started when we got to the theatre.

我们到剧场时戏已经开演了。

II. The Passive 被动语态完成时被动语态的构成形式如下：

Have/has/had+v-ed2 →have/has/had+been+v-ed2

This part of the seabed has been explored many times.这部分海底已经多次探索过了。

Some kinds of special equipment for space travel have been developed over the last few years.

过去几年中研制出了几种用于宇航的专用设备。

Five units of this textbook had been studied by the end of last month.

到上个月底，已经学了这本书的五个单元。

Exercise

Exercise 1 Put in the right forms of “have”

1) Electricity power become a very important part of our life .

2) Mr White designed(设计) a new kind of machine.

3) We studied medical science for many years .

4) When the traveller reached the railway station ,the train already left.

Exercise 2 Combine the left with the right ,making as many sensible sentences as possible. 1)Scientist have studied the problem two years ago

of the future transport

2) They designed the new equipment for many years

3) Great progress has been made in China by 1998

4) The chemistry lab was built in 1997

5)More than 20 electric cars had been since 1999

Produced in this factory

Exercise 3 Make the words in italics the subjects. Leave out the by-phrase.

1)People have saved much parking space in cities by using small cars.

2)They had built two sets of roads by 1999.

3)He has collected much useful information about these planets since 1234.

4)People had not explored outer space before 1957.

Exercise 4 Translate the Chinese in brackets into English .

1)By that time this car (已经行使了200公里)

2)Those travellers (已经被带到一座大旅馆去了)

3)By the end of last year our college (已经生产了两台计算机)

4)Much information (已被送回地球)since the spacemen began their exploration on the moon .

5)The telephone (已被广泛使用)since its invention.