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语篇训练卷(十)
Unit 4 Warming Up & Reading
阅读理解
A
The earth is the only planet that scientists think has life. Why does the earth have life while the other planets don’t? For one thing, the earth is just the right temperature. As the third planet from the sun, the earth seems to be just the right distance away. The planets which are closer to the sun are so hot that their surfaces bake(烘烤)in the sun. The farthest planets are cold balls.
When the earth developed—which scientists believe may have happened about 4 billion years ago—many gases covered the earth. The gases caused the earth to be hot. But something wonderful happened. The temperature was just right for thick clouds to form. It rained very hard for a very long time. This gave the earth its oceans. Water made it possible for plants to grow. The plants created oxygen in the atmosphere.
