Without air, there would be no fire. There would be no cars or trucks, since motors need air in order to work.

Without air, there would be no wind or clouds. There would be no weather, as we know it.(结构：状、意义：定) The night time would be very cold and the days very hot. We would be forced to seek shelter from the sun, as there would be no atmosphere to protect us from the suns deadly rays.

The atmosphere is all the air surrounding the earth. Atmospheric pressure is the weight of all that air against the surface of the earth. If we did not have atmospheric pressure, we could not have automobile tires. The tires would burst if they did not have the pressure of the atmosphere against their surfaces.

Large and powerful,(being large and powerful) the atmosphere consists of an ocean of gases hundreds of miles high. It presses down on our bodies with a force of more than fourteen pounds per square inch. The narrow column of air which rests upon our shoulders weighs almost 2,000 pounds. But our bodies are built in such a way that this weight does not crush us.

In this huge ocean of air there is more energy than in all the coal, oil, and gas that we have on earth. Electrical energy is collected in the atmosphere as water is collected and stored in a dam. The existence of electricity in the air has been known for centuries. Men have gazed in wonder at the bright patterns of lightning in storm clouds. But a thorough study of electricity in the atmosphere was not possible until the development of radio and radar.
one scientist, Dr. Sydney Chapman, has tried to explain the electric field which surrounds the earth. He believes that the great storms on the sun create large amounts of electric energy. This energy is contained in a very light gas called hydrogen. The earth pulls the gas toward it, and a ring is formed around the earth several thousand feet above its surface. The great space ring is a powerful current of electrical energy. Sometimes the ring comes down and curves into the lower atmosphere, causing strange electrical effects.

Dr. Chapmans ideas explain many things. It has long been known that there is an electric field inside the earth. It(electric field) moves in much the same manner as the electric energy contained in the atmosphere. Scientists now believe that the electric energy in the atmosphere causes the electric energy inside the earth to flow.

If we can learn to control the energy in the atmosphere, we will have an unending supply of energy. Many scientists are trying to learn how to control it. In the meantime, even those of us who are not scientists have begun to pay attention to air. We realize that air does not contain the same elements that it contained years ago. Automobiles, airplanes, factories, and atomic explosions have added dust and waste gases to the atmosphere. It is time to learn how to protect our atmosphere, the roof over the world of man.

If I were you, I would give up smoking.
Were I you, I would give up smoking.
If you went now, you could see him.

If you had taken my advice, you would have got success.
Had you taken my advice, you would have got success.
It is important that our earth should be protected form pollution.

It is necessary that he read English every day.

条件从句， ＋主句

If there were no air, there would be no wind.

If …, … .

与现在相反：If+过去式， would (should) + 动词原形

If I were you, I would reconsider their proposal.

If the manager were here, he might make a decision.

与过去相反：

If+过去完成时(had+过去分词), should (would) + have +过去分词

If I had left a little earlier, I would have caught the train.

If he hadn’t been ill, he might have come.

与将来相反：

If+should +动词原形 (were+动词不定式)，should (would) + 动词原形

If he should fail, we should encourage him to try again.

If I were to do it, I would do it in a different way.

省略条件从句中的if

如果条件从句的谓语包含有had, should 或were，有时if 可以省略。

If he had not been ill, he might have come.

Had he not been ill, he might have come.

If I were to do it, I would do it in a different way.

Were I to do it, I would do it in a different way.

If it should rain tomorrow, what could we do?

Should it rain tomorrow, what could we do?

主语从句

下列结构中，从句用“动词原形”或“should+动词原形”

It is necessary (important, essential, advisable, ordered, proposed, requested, suggested, recommended, demanded ) that…

It is necessary that he __ there at once.

Send; sent; is sent; be sent

Send; sends; sent; be sent

It is suggested that the meeting (should) be held at some other time.

宾语从句

下列动词后面的宾语从句中，谓语动词用“动词原形”或“should+动词原形”

suggest, insist, recommend, propose, require, request, demand

They demanded that the right to vote be given to every adult.

We insisted that Mr. Brown chair the meeting.

Wish后的宾语从句表未实现的主观愿望

I would rather _walk__ (walk) home.

I wish I were as young as you.

We wish he hadn’t gone.

It is time that…

It is time _to go_ (go) to school.

巩固练习

They wish there __ (be) much water and air on the moon.

If fish were the best brain food, many people _would eat_ (will, eat) more fish than usual to improve their memory.

If we _did not have_ (not, have) air, there would be no sound.

It is recommended that he _apply_ (apply) for a position in an international bank.

If we _had been_ (have, be) more careful, such mistakes could have been avoided.

If her pains _had been caused_ (have, cause) by a heart attack and not by panic, she would probably have been operated on in the hospital.

Without air, the night time _would be_ (will, be) very cold and the days very hot.

I would rather he _bought_ (buy) the house next year.

I wish man _could build_ (can, build) a nest which is as good as one built by birds.

It is desirable that both the father and mother _earn_ (earn) money for the family.

If we ______ (not, have) air, there would be no sound. （8B 2000上）

If we did not have atmospheric pressure, we __could not have__ (can, not, have) automobile tires. (8B 2003 下)

要是昨天他早一点回到家，他的女儿就不会把他的手表拆了。（2000上）

If he had come home a little earlier yesterday, his daughter would not have taken apart his watch ．

wish, would rather (sooner)后的虚拟语气

I didn‘t go to the party, but I do wish I ___(be) there. (2002 下)

We often hear old people wishing they ___ young again .

[A] are [B] were

[C] had been [D] will be

(2001 上)

从句中用should加动词原形的虚拟语气，其中should可省略。

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