油样和气样应尽快进行分析，为避免气体逸散，油样保存期不得超过7天，气样保存期应更短些
题型：判断题
问题：
油样和气样应尽快进行分析，为避免气体逸散，油样保存期不得超过7天，气样保存期应更短些（）
题型：判断题
第三部分阅读理解（共20小题；每小题2分，满分40分）
A
Forests have always been useful and important to man who make use of them in many ways. Every day trees are serving man everywhere. Trees supply man with fruits and building materials in the form of wood, without trees it would be impossible to build houses, boats, bridges and so on. Furniture such as desks, chairs and beds is made of wood, trees can stop man from terrible heat. They're also useful in preventing good and rich top soil from being washed away during heavy rains.
If there were no trees, heavy rains would wash away the rich surface soil that is so important to plants. The result is that the land will become a desert. There are plenty of desert areas in the world. A long time ago these desert areas used to be very rich areas, but man in the past had no enough knowledge about science of nature, they cut down too many trees in the area where they lived and never planted new ones. By and by the rich surface soil was blown and washed away by strong winds and heavy rains. In the end the rich land changed into useless deserts where nothing could grow.
56 . According to the passage,__________.
A. a long time ago, man didn't know how to make use of wood
B. trees are not as useful as they were in the past
C. trees were more found in the past than they are today
D. people have always found trees useful
57. "Top soil" means____________and is .
A. useless soil; of no use for plants
B. soil on the surface of the earth; good for plants
C. soil found under the earth; found under the roots of trees
D. dry soil in the desert areas; bad for plants
58. Some deserts were once__________.
A. very good lands B. covered by ice C. very cold D. dry and useless
59. If there were no trees,______________.
A. the land would become better B. heavy rains would be very clean
C. the rich soil couldn't be kept D. there wouldn't any plants
60. From the passage, we know that man must__________.
A. do 
nothing to keep the balance of nature
B. take his best to keep the balance of nature
C. try his best to keep the balance of nature
D. do his best to stop the balance of nature