61、It can be inferred from thefirst paragraph that _________

　　A.water vapor is an air pollutant in localized areas

　　B.the definition of air pollution will continue to change

　　C.a substance becomes an air pollutant only in cities

　　D.most air pollutants today can be seen or smelled

　　62、In what way can naturalpollutants play an important role in controlling air pollution?

　　A.They function as part of a purification process.

　　B.They are dwarfed by the pollutants produced by human activities.

　　C.They are less harmful to living beings than are other pollutants.

　　D.They have existed since the Earth developed.

　　63、According to the passage,the numerical value Of the concentration level of a substance is only useful if

　　A.the other substances in the area are known

　　B.it is a localized area

　　C.it can be calculated quickly

　　D.the naturally occurring level is also known

　　64、Which of the following isbest supported by the passage?

　　A.To effectively control pollution, local government should regularlyrevise the air pollution laws.

　　B.One of the most important steps in preserving natural lands is tobetter enforce air pollution laws.

　　C.Scientists should be consulted in order to establish uniform limitsfor all air pollutants.

　　D.Human activities have great impact on air pollution.

　　65、The passage mainlydiscusses _________

　　A.the economic impact on air pollution

　　B.how much damage air pollutants can cause

　　C.what constitutes an air pollutant

　　D.the quantity of compounds added to the atmosphere

　　答案解析：

　　61-65 BADDB