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Astronomy
完型填空：每小题2分,共20分
Planets are the largest objects that circle around the stars. They may be rocky, 21 the earth, or made mostly of gas and 22 , like Jupiter. The word planet is Greek 23 “wanderer”. The name comes from the 24 planets appear to move against the stars over time. It is thought that the planets formed at about the same 25 as the sun. Over several million years, the dust and gas 26 together to form the planets and moons. Solider rocks gathered near the sun and lighter gases farther 27 .
Our planet, the earth, is a large 28 of rocks and metals covered with water and soil. It 29 a group of nine planets that move around a star called the sun. It is 30 by a blanket of gases called the atmosphere, has one moon, and as far as we know, is the only planet that supports life.
21. A. like B. as C. such as D. for example
22. A. liquid B. solid C. rock D. water
23. A. towards B. to C. as D. for
24. A. method B. way C. manners D. means
25. A. time B. place C. reason D. year
26. A. formed B. put C. worked D. gathered
27. A. in B. out C. up D. down
28. A. cloud B. world C. ball D. box
29. A. makes up B. breaks up C. belongs to D. comes to
30. A. forced B. floated C. buried D. surrounded
A
Even if you are a good high-jumper, you can jump only about seven feet off the ground. You cannot jump any higher because the earth pulls you hard. The pull of the earth is called gravity.
You can easily find out the pull of the earth. If you weigh yourself, you will know how much gravity is pulling you.
Since there is gravity, water runs downhill. When you throw a ball into the air, it falls back down. Because of gravity, you do not fall off the earth as it whirls (旋转) around.
Then, can we get away from the earth and go far out into space? Now you can do it, because spaceships have been invented. Then spaceship will go so fast that it can escape the earth’s gravity and carry you into
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