问题 问答题

某热电厂地处多雨地带,所使用的燃料煤中含少量硫,燃烧的气体未经处理即排往空中,又有部分发电用水未经冷却排入河流.观察其下游几十公里的河水中鱼类几乎绝迹,试解释出现这种现象的原因(必要时写出有关反应的化学方程式).

答案

鱼类大量死亡的原因是:煤中的硫燃烧后生成SO2气体,SO2被氧化成SO3(2SO2+O2

 粉尘等催化剂 
.
 
2SO3),并与水化合生成H2SO4(SO3+H2O═H2SO4).酸雨直接降落或排放到河流中,鱼类要在一定的PH值范围内的水中才能生存,时间一久,河水PH值减小,酸度增大,使鱼类几近绝迹;其次是热电厂发电排出的废水未冷却直接排放河中,使水温超过鱼类适宜的水温条件,水中溶氧量减少,不适于鱼类生长,废水中其它化学毒物也直接危害鱼类生存.

故答案为:煤中的硫燃烧后生成SO2气体,SO2被氧化成SO3(2SO2+O2

 粉尘等催化剂 
.
 
2SO3),与空气中水形成酸雨(SO3+H2O═H2SO4),流入河内不适于鱼类生长;废水使河水温度升高,水中溶氧量减少,不适于鱼类生长,废水中其它化学毒物也直接危害鱼类生存.

单项选择题
阅读理解

第三部分阅读(共两节,满分40分)

第一节阅读理解(共15小题;每小题2分,满分30分)

阅读下列短文,从每题所给的A、B、C和D项中,选出最佳答案。

We’ve talked about snails (蜗牛) and their slow move. But much of the time snails don’t move at all. They are in their shells (壳) —sleeping.

Hot sun will dry out a snail’s body. So at the least sign of hot sun, a snail draws its body into his shell. A snail will die in a heavy rain. So when it rains, a snail does the same thing, too. A snail can sleep for as long as it needs to. It spends all  the winter months in its shell, asleep.

In the spring the snail wakes up. Its body, about three inches long, comes out from the shell. When hungry, the snail  looks for food. Its eyes, at the end of the top feelers (触角), are very weak. But its sense (感觉) of smell is very strong. It helps the snail to find food and the new greens.

A snail’s mouth is no bigger than the point of a pin (大头针). Yet it has 256,000 teeth! The teeth are very small, and you can’t see them. If you put a snail in a hard paper box, it will eat its way out! And if a snail wears out its teeth, it will grow new ones.

51. A snail _________.

A. moves more slowly at night        B. has thousands of  feet

C. doesn’t move at all                     D. sleeps much of the time

52. In the sentence “A snail draws its body into its shell”,  the word “draw” means _____.

A. to make with a pencil        B. to push      C. to pul     D. to move away

53. From the story, we know _________.

A. a snail’s shell is very thin           B. a snail can’t see well

C. a snail’s nose is quite short        D. a snail’s body changes                                    in different seasons

54. A snail goes to sleep when _____.

A. it feels hungry   B. it is put into a paper box  C. spring is coming   D. it rains heavily

55. Which of the following is wrong?

A. In winter the snail doesn’t eat or move. 

B. A snail doesn’t like living under the sun.

C. The snail’s teeth can’t be worn out.      

D. The snail’s nose helps to find food.