英语是欧盟和许多国际组织与英联邦国家的官方语言之一，精品小编准备了高中二年级必修三英语Unit4知识点，希望你喜欢。

“be+to”还可以表示以下含义：

表示可能性，相当于can,主要用于疑问句和否定句。表示命令，意为“必须，不得不”，意思等同于must, have to，表示假设。表示“命运注定……”，通常用于过去时。

How am I to know what has become of him?我怎么知道他的遭遇如何呢? Certain skills must be learned if one is to use English well.如果想要用好英语，某些技巧是必须学的。

He was never to see his wife again.他注定再也见不到他妻子了。

Were we to offer you more money, would you stay?如果我们给你加钱，你愿意留下吗?

单项填空 In dry weather the flowers will have to be watered if they           .    A. have survived              B. are to survive C. would survive              D. will survive 解析:选B。考查真实条件句。are to survive在此处并不表示将来，而表示“期望”。

22.  lay

lay the table摆桌子 lay eggs下蛋;产卵 lay oneself down to sleep躺下睡觉 注意下列词形变化： lay-laid-laid-laying放置;产卵 lie-lay-lain-lying躺;位于 lie-lied-lied-lying撒谎

23. But when I tried to step forward, I found I was carried twice as far as on the earth and fell over.而当我试着向前迈步的时候，我发觉我被送出去很远，步子的跨度竟是地球上的两倍，因而我摔倒了。 twice as ...as ... 是……的两倍

拓展 英语中的倍数表达法： 倍数+as +adj./adv.+as 是……的几倍 倍数+adj./adv.的比较级+ than 比……(多/大)几倍 倍数+ the +表示长度/高度/宽度等的名词+ of是……长度/高度/宽度的几倍，此结构中常用的名词有：size, height, weight, length, width, depth等。

This ruler is three times as long as that one. =This ruler is twice longer than that one. =This ruler is three times the length of that one.这把尺子是那把的三倍长。 There are four times as many students as we expected. 到的学生是我们预计的五倍。

(1)翻译句子   这个房子是那个的三倍大。 (2)完成句子 到的客人是我们预计的两倍。 There are                                                 we expected . 答案：(1)This house is three times as big as that one./This house is twice bigger than that one./This house is three times the size of that one. (2)twice as many guests as

24. 回归课文                                     P.25  Reading    HOW LIFE BEGAN ON THE EARTH

No one knows exactly how the earth began, as it happened so long ago. However, according to a widelyaccepted theory, the universe began with a "Big Bang" that threw matter in all directions. After that, atoms began to form and combine to create stars and other bodies.

For several billion years after the "Big Bang", the earth was still just a cloud of dust. What it was to become was uncertain until between 4.5 and 3.8 billion years ago when the dust settled into a solid globe. The earth became so violent that it was not clear whetherthe shape would last or not. It exploded loudly with fire and rock. They were in time to produce carbon, nitrogen, water vapour and other gases, which were to make the earth's atmosphere. What is even more important is that as the earth cooled down, water began to appear on its surface.          Water had also appeared on other planets like Mars but, unlike the earth, it had disappeared later. It was not immediately obvious that water was to be fundamental to the development of life. What many scientists believe is that the continued presence of water allowed the earth to dissolve harmful gases and acids into the oceans and seas. This produced a chain reaction, which made it possible for life to develop.          Many millions of years later, the first extremely small plants began to appear on the surface of the water. They multiplied and filled the oceans and seas with oxygen, which encouraged the later development of early shellfish and all sorts of fish. Next, green plants began to grow on land. They were followed in time by land animals. Some were insects. Others, called amphibians, were able to live on land as well as in the water. Later when the plants grew into forests, reptilesappeared for the first time. They produced youngenerally by laying eggs. After that, some huge animals, called dinosaurs, developed. They laid eggs too and existed on the earth for more than 140 million years. However, 65 million years ago the age of the dinosaursended.  Why they suddenly disappeared still remains a mystery. This disappearance made possible the rise of mammals on the earth. These animals were different from all life forms in the past, because they gave birth to young baby animals and produced milk to feed them.          Finally about 2.6 million years ago some small clever animals, now with hands and feet, appeared and spread all over the earth. Thus they have, in their turn, become the most important animals on the planet. But they are not looking after the earth very well. They are putting too much carbon dioxide into the atmosphere, which prevents heat from escaping from the earth into space. As a result of this, many scientists believe theearth may become too hot to live on. So whether life will continue on the earth for millions of years to come will depend on whether this problem can be solved.

continued story   连载小说[故事]

P. 30 A VISIT TO THE MOON

Last month I was lucky enough to have a chance to make a trip into space with my friend Li Yanping, an astronomer. We visited the moon in our spaceship!       Before we left, Li Yanping explained to me that the force of gravity would change three times on our journey and that the first change would be the most powerful. Then we were off. As the rocket rose into the air, we were pushed back into our seats because we were trying to escape the pull of the earth's gravity. It was so hard that we could not say anything to each other. Gradually the weight lessened and I was able to talk to him. "Why is the spaceship not falling back to the earth? On the earth if I fall from a tree I will fall to the ground." I asked. "We are too far from the earth now to feel its pull," he explained, "so we feel as if there is no gravity at all. When we get closer to the moon, we shallfeel its gravity pulling us, but it will not be as strong a pull as the earth's." I cheered up immediately and floated weightlessly around in our spaceship cabin watching the earth become smaller and the moon larger.       When we got there, I wanted to explore immediately. "Come on," I said. "If you are right, my mass will be less than on the earth because the moon is smaller and I will be able to move more freely. I might even grow taller if I stay here long enough. I shall certainly weigh less!" I laughed and climbed down the steps from the spaceship. But when I tried to step forward, I found I was carried twice as far as on the earth and fell over. "Oh dear," I cried, "walking does need a bit of practicenow that gravity has changed." After a while I got the hang of it and we began to enjoy ourselves.       Leaving the moon's gravity was not as painful as leaving the earth's. But returning to the earth was very frightening. We watched, amazed as fire broke out on the outside of the spaceship as the earth's gravity increased. Again we were pushed hard into our seats as we came back to land. "That was very exhausting but very exciting too," I said. "Now I know much more about gravity! Do you think we could visit some stars next time?" "Of course," he smiled, "which star would you like to go to?"

P. 66.                  CAUGHT BY A BLACK HOLE

The spaceship warned Li Yanping and me to be ready as we were approaching (靠近) the "black hole". We could see some faint lights around what looked like an empty space. Li Yanping said, "That empty hole is like a mouth always needing to be fed. Those lights are things that are being pulled into it by the gravity of the hole." We watched with interest and amazement at the lights which seemed to be going fainter and fainterround the edge of the black hole. Just then the lights on our spaceship went out and the computer stopped working. What was happening? I tried to turn the spaceship away from the hole but it would not move. Would it eat us too?       Suddenly the spaceship jumped and began to move round the edge of the hole too. The gravity of the "black hole" was pulling us into its "mouth". As the spaceship moved round the black hole, I felt rather sick. My mouth went dry and I closed my eyes. All the storiesabout what happened when you were caught by the gravity of a "black hole" seemed to be true.       But then the spaceship jumped again. This time it moved sideways and away from the edge of the "black hole". Someone watching me would have seen the spaceship flying like a bird away from the "black hole".But we felt nothing. At last we were able to look around us. Luckily the computer had started working again. We realized that we had discovered something new about "black holes". If you go inside the edge of a "black hole", it will "eat" you and there is no escape; but if you do not, you may have an opportunity to escape. How exciting!

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