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。
答案简析
1.A。空气通常被看成是裹在地球外表的毯子。
2.B。
3.B。more than固定短语“不仅仅”。
4.D。根据常识，洞穴当然在地球的深处。
5.C。固定短语be mixed with。
6.A。与下文中above的意思相反，即在地表之下。
7.B。人们误以为，事实并非如此。
8.A。他们“称之为……”told , said 都不准确，而name的时态不对。
9.C。这里的as有“随着”的意思，相当于when 。
10.C。此处decided意为“得出结论”。believe很具有迷惑性，但其时态不对。特别要当心呀。
11.B。最终得出结论。另外三个选择都很显然不对。
12.D。 either用于否定句，“也不”的意思。
13.C。 无论是语法结构还是意思只有In fact对。
14.D。 尽管它们不是元素，但他们是人类环境的三个主要部分。
15.D。 你会对它们了解得更多。