某肥牛育肥基地及屠宰加工厂可行性研究报告精品.doc
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1、one knows exactly how the earth began, as it happened so long ago. However, according to a widely accepted theory, the universe began with a “ Big Bang “ that threw matter in all directions. After that, atoms began to form and combing to create stars and other bodies.For several billion years after
2、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 earthenware became so violent that it was not clear whether the shape would last or not. It exploded loudly with f
3、ire and rock. They were in time to produce carbon, nitrogen , water vapour and other gases , which were to make the earths atmosphere. What is even more imprtant 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
4、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 persence of water allowed the earth to dissolve harmful gases and acids into the oceans and seas. This produced a chain reac
5、tion, 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. Ne
6、xt, 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, reptiles appeared for the first time. They produced young generally by laying
7、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 dinosaurs ended. Why they suddenly disappeared still remains a mystery. This disappearance made possible thief r
8、ise of mammals on the earth. These animals were different from all life forms in the past, because they Gavin birth to young baby animals and prodeced milk to feed them.Finnally about 2.6 million years ago some small celver animals, now with hands and feet, appeared and spread all over the earth. Th
9、us they have, in their turn, become the most important animals on the planet. But they no they looking after the earth very well. They are putting too much carbon dioxide into the atmosphere, which prevenrs heat from escaping from the earth into space. As a result of this, many scientists believe th
10、e earth may bcome 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.A visit to the moonLast month I was lucky engough to have a chance to make a trip into space with my friend Li Yanping, an astronomer. We v
11、isited the moon in our spaceship!Before we leave, Li Yanping explained to me that the forece of the 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 w
12、ere trying to escape the pull of the earths 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 ground.” I asked. “ W
13、e 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 shall feel its gravity pulling us, but it will not be as strong a pull as the earths. “ I cheered up immediately and floated weightlessly around in our
14、 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
15、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 practice now that gravity has changed.”
16、 After a while I got the hang of it and we began to enjoy ourselves.Leaving the moons gravity was not as painful as leaving the earths. But returning to the earth was very frightening. We watched, amazed as fire broke out on the outside of the spaceship as the earths gravity increased. Again we were
17、 pushed back 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 bisit some stars next time?” “Of course,” he smiled, “ which star would you like to go to?”Caught by a black holeThe spacesh
18、ip warned Li Yanping and me to be ready as we were approaching 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 thins that are being pulled into time by the gravity o
19、f the hole.” We watched with interest and amazement at the lights which seemed to be going fainter and fainter round the edge of the black hole. Just then the lights on our spaceship went our the and the computer stopped working. What was happening? I tried to turn the spaceship away from the hole b
20、ut it would not move. Would it eat us too?Suddenly the spaceship jumped and began to move round the edge of trhe 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
21、 stories about what happened when you were caught by the gravity of a “black hole” seem to be true.But then the spaceship jumped again. This time it moved sideways and away from this edge of the “black hole”. Someone watching me would have seen the spaceship flying like a bird away from the “black h
22、ole”. 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 hole”. 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 ha
23、ve an opportunity to escape. How exciting!Unit 5A trip on “ The True North”Li Daiyu and her cousin Liu Qian were on a trip to Canada to bisit their cousins in Montreal on the Atlantic coast. Rather than take the aeroplane all the way, they decided to fly to Vancouver and then take the train west to
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