The water and the land are thought part of the earth surface (表面). The air is 1 thought a kind of blanket (毯子) 2 the earth. But it is 3 than that. Maybe you have been in a cave (洞穴) 4 in the earth. Did you think about the air that was in the cave? The land has some air mixed in it. Air is even mixed 5 the water in the sea. These examples show that some air is 6 the earth’s surface as well as above it.

　　Men once 7 that there were four basic things from which everything else was made. They 8 these things-earth, fire, air and water the four elements (元素). 9 man made more observations, they 10 that fire was not an element. 11 they concluded (得出结论) that land, air and water were not elements, 12 .

　　13 , there are more than 100 elements from which scientists believe all things are made. 14 land, air and water are not elements, they are three main parts of man’s environment (环境). You will 15 more about them as you study the earth.

　　1. A. usually B. seldom C. never D. sometimes

　　2. A. above B. around C. across D. among

　　3. A. better B. more C. less D. worse

　　4. A wide B. high C. long D. deep

　　5. A. at B. in C. with D. to

　　6. A. below B. before C. between D. beside

　　7. A. found B. thought C. knew D. understood

　　8. A. called B. told C. name D. said

　　9. A. That B. For C. As D. So

　　10. A. believe B. planned C. decided D. want

　　11. A. End B. At last C. Hardly D. Nearly

　　12. A. too B. neither C. also D. either

　　13. A. True B. Read C. In fact D. Correctly

　　14. A. When B. As C. Since D. Though

　　15. A. exam B. study C. exercise D. know

　　名师点评

　　本篇着重介绍与人们的生活休戚相关的地球、水、空气以及人们对它们的认识过程。这是一篇说明文，文章浅显易懂。