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        The earth is the fifth largest of the eight planets in our solar system (太阳系) . Scientists believe that the earth is the only planet that 1 life. It's home to millions of species (物种) 2  us—humans!

        The solar system is like a neighborhood where the earth is located (位于) . The solar system is 3  of other planets,moons,and many other things. The moon travels a-round the earth. Scientists believe that the moon was once part of the earth 4 may have been broken off the earth during a massive collision (剧烈的碰撞) . The moon is much 5 than the earth,about 1/4 of the diameter (直径) of the earth.

        The earth is also known as the blue planet. 6 ?The reason is that most of the earth's surface 7 water that makes it look blue in color from space. A blanket of gases surrounds the earth. This layer is called the earths atmosphere (大气层) .Without the atmosphere life on earth is 8 . It gives us air,water,heat,and 9  us against harmful rays from the sun and against meteorites (陨星) .

        Planet earth is really,really old. It was formed 4. 54 billion years ago and life started to 10 about billions of years ago. Modem humans showed up on the earth about 200,000 years ago.

() 1. A. produces   B. develops   C. provides   D. supports

() 2. A. including   B. included   C. holding   D. except

() 3. A. filled   B. afraid   C. full   D. made

() 4. A. or   B. but   C. though I) , and

() 5. A. bigger   B. lighter   C. smaller   D. heavier

() 6. A. What   B. Why   C. How   D. Where

() 7. A. is covered by   B. is born with   C. is known for   D. is thirsty for

() 8. A. impossible   B. probably   C. unable   D. difficult

() 9. A. sends   B. protects   C. offers   D. fights

() 10. A. change   B. stay   C. stand   D. appear

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