15. C。是她协助抓住小偷的。

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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.

14.　 D。in a way 固定短语，“在某种程度上”。 In a word “总而言之”；in a shop “在商店里”；in a moment 一会儿。

13.　 C。应该是在小偷被抓之后，所以这个最为准确。

12.　 A。run after 追赶，跟在后面跑。

11.　 D。get out 出来。如果要选C得加一个宾语the car 。

10.　 B。就在这时警察也过来了。其他选项所表达的时间太慢了，根据上下文可知，都是不可能。

9.　　　 D。从下文可知，小汽车是停下来了，而不是“走过”或“转弯”

8.　　　 C。虽然自己没伤着，但自行车还是被一辆小汽车给撞了。

7.　　　 C。看她的身后。

6.　　　 B。警笛越来越近。Bigger and bigger很容易被当选，但形容声音最好用louder and louder。