12．There are many ways of putting out a fire．You may have seen people put out burning cigarettes by stepping on them．Stepping on cigarettes shuts off the air and puts out the fire．
Many fires are put out with water．Water cools the materials that are burning．It helps make the fire die out．Some of the water is changed into steam when it strikes the hot fire．The steam keeps air from the fire and helps put it out．
Some fires cannot be put out with water．Suppose a tank full of gasoline（汽油）is on fire．Gasoline is lighter than water．If you poured water into the tank of gasoline，the water would sink to the bottom of the tank．The gasoline would float on top of the water on the fire and flow over the edge of the tank．Then the fire would spread．Gasoline fires should be put out with sand or with chemicals of some kind，such as that used in some fire extinguishers．
36．People often put out burning cigarettes by stepping on them．This is becauseC．
A．the burning cigarettes are too hot to touch
B．they have no other way
C．it shuts off the air and makes the fire go out
D．it helps to stop smoking
37．B the fires can be put out with water．
A．All of B．Some of C．None of D．Few of
38．According to paragraph 2，what will happen to the water if it is poured on the fire？D
A．All of the water will disappear．
B．Most of the water will flow away．
C．The water will be absorbed by the fire．
D．Some of the water will turn into steam and keep air from the fire．
39．Gasoline fire should be put outD．
A．with hot water
B．with nothing but sand
C．only with some chemicals
D．with sand or chemicals
40．Why will the water sink to the bottom of the tank when it is poured into the tank of gasoline？C
A．Because gasoline is much hotter than water．
B．Because water can burn．
C．Because gasoline is less heavy than water．
D．Because water cannot flow as quickly as gasoline．
分析 这篇文章主要讲述了灭火有很多方法，有的火可以用水熄灭，有的火不能用水熄灭，有的火要用沙子或某些化学物质来灭火．作者写这篇文章是为了教会我们如何去灭火，让我们能遇到灾情时做出正确的解救措施．
解答 36．C细节理解题，由第一段Stepping on cigarettes shuts off the air and puts out the fire．可知踩在烟头上隔绝空气使火熄灭，故选C．
37．B细节理解题，由第二段Many fires are put out with water．可知许多火可以用水熄灭，故选B．
38．D细节理解题，由第二段Some of the water is changed into steam when it strikes the hot fire．The steam keeps air from the fire and helps put it out．可知一些水遇到火时变成了蒸汽，蒸汽隔绝空气使火熄灭，故选D．
39．D细节理解题，由最后一段Gasoline fires should be put out with sand or with chemicals of some kind，such as that used in some fire extinguishers．可知汽油点燃的火应用沙子或某种化学物质熄灭，故选D．
40．C细节理解题，由最后一段Gasoline is lighter than water．If you poured water into the tank of gasoline，the water would sink to the bottom of the tank．可知汽油比水轻用水汽油会在水面上继续燃烧，故选C．
点评 健康环保类文章常是介绍科学知识、生活常识和环境保护方面的短文．阅读此类短文要以现象或事物为中心进行思考，理解现象产生的原因、条件和客观规律等．
