We know that trees are useful in our everyday life. They   1  us many things, such as wood, oxygen, rubber, medicines and many other things. They can  2  tell us a lot about our climate. The following are the reasons. If you   3  a tree, you can see that it has many rings. Most trees grow one new ring   4  year. Because of the reason, we know   5  a tree is. A tree over a hundred years old means that it has more than a hundred   6 . When the climate is dry or very cold, the trees do not grow very much and their rings are usually   7 . When it is wet and warm, the rings are much thicker. If the rings are suddenly very thin or suddenly very thick, this means that the   8  changed suddenly. If we look at the rings on this tree, we can learn about the   9  for a hundred years. We can see  10  our climate is changing today.

　　When cold weather comes, many birds move to warmer places to find food. Some fishes give birth in warm water and move to cold water to feed. The most famous migration（迁移）is probably the migration of the fish, which is called“salmon”. This fish is born in fresh water but it travels many miles to salt water. There it spends its life. When it is old, it returns to its birthplace in fresh water. Then it gives birth and dies there. In north Europe, there is a kind of mouse. They leave their mountain homes when they become too crowded. They move down to the low land. Sometimes they move all the way to the seaside, and many of them are killed when they fall into the sea.

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(2)The fish called“salmon”spends long life in ________.

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A．they give birth

B．the weather is bad

C．the places get too crowded

D．they haven't enough food

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A．Animals move in order to find food more easily.

B．The migration of the fish called“Salmon”is the most famous migration.

C．Living things more from one place to another because they like to travel.

D．Sometimes we know why and how living things move from one place to another, but sometimes we don't.

阅读理解

　　The earth is not the only body that travels around the sun. With it are eight other planets, fellow members of the sun' s family. Two of them are nearer while the other six are farther from the sun than the earth is. The farther they are, the longer trip they make around the sun. People noticed long ago that these traveling bodies moved around in the sky in certain paths.

　　We know that every little hit of matter in the universe pulls upon every other hit of matter. The pull between two bodies is proportional (成比例的) to the product (乘积) of their masses. Because the sun is so large, the pulls between the sun and planets are thus great. If it were not for these pulls, the planets would fly off into space. In the same way there is a pull between the earth and the moon, which keeps the moon traveling in its orbit (轨道) around our planet, the earth. The pull holds you to its surface, and pulls back the ball which you throw into the air. Of course the ball also pulls on the larger earth but the earth is so much larger that the pull is not noticed.

(1) The earth travels a larger circle around the sun than ________ .

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A. six of the other planets

B. two planets in the same family

C. most planets in the universe

D. the moon

(2) The planets move around the sun because of ________ .

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A. the gravity (引力) of the sun only

B. the pull of the planets on one another

C. the pull between the planets and the sun

D. the proportional gravity

(3)If objects (物体) didn't have gravity, ________ .

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A. the earth would not travel in the space

B. the moon would move away from the earth

C. the sun would not exist

D. the planets of the sun family form another family

(4) Which of the following pictures shows correctly the pull between the objects?

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(5) The sun's family has ________ members in this text.

A. two

C. nine

D. eight

B. six

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