reading from Dec.1997

[John750]

(Dec.1997 N.America)

Questions 41 - 50 refer to the following passage

 

A useful definition of an air pollutant is a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals vegetations, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled-a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

 

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentrations of these pollutants were altered by various chemical reactions; they became components in biogeochemical cycle. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil on a global basis, nature's output of these compounds dwarfs that resulting form human activities. However, human production usually occurs in a localized area, such as a city.

 

In this localized regions, human output may be dominant and may temporarily overload the natural purification scheme of the cycle. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, ahs a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

 

41. What does the passage mainly discuss?

 

A. The economic impact of air pollution

B. What constitutes an air pollutant

C. How much harm air pollutants can cause

D. The effects of compounds added to the atmosphere

 

50. Which of the following is best supported by the passage?

 

A. To effectively control pollution local government should regularly review their air pollution laws.

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

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

D. Human activities have been effective in reducing air pollution.

 

Thanks a lot!

 

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[bhavinv]

Here are the answers to your questions

 

(Dec.1997 N.America)

Questions 41 - 50 refer to the following passage

 

A useful definition of an air pollutant is a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals vegetations, or materials adversely. Air pollution requires a very flexible definition that permits continuous change. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled-a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

 

Many of the more important air pollutants, such as sulfur oxides, carbon monoxide, and nitrogen oxides, are found in nature. As the Earth developed, the concentrations of these pollutants were altered by various chemical reactions; they became components in biogeochemical cycle. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil on a global basis, nature's output of these compounds dwarfs that resulting form human activities. However, human production usually occurs in a localized area, such as a city.

 

In this localized regions, human output may be dominant and may temporarily overload the natural purification scheme of the cycle. The result is an increased concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0.08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however, ahs a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

 

41. What does the passage mainly discuss?

 

A. The economic impact of air pollution

B. What constitutes an air pollutant

C. How much harm air pollutants can cause

D. The effects of compounds added to the atmosphere

 

I think B is correct.

 

50. Which of the following is best supported by the passage?

 

A. To effectively control pollution local government should regularly review their air pollution laws.

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

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

D. Human activities have been effective in reducing air pollution.

 

C should be the correct answer.

 

Thanks a lot!

 

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[John750]

Hi bhavinv, thanks for your reply.

The given answers are

41:B

50:D

 

I also pick C for 50. I just don't answer why D is the answer.

[John750]

can anyone out there tell me why D is correct for question 50?

thanks a lot!

[FinMaster]

Hi John750,

 

I would pick B in 41 and D in 50. Why D in 50? The first paragraph describes how technology our knowledge about different harmful substances. Since technology is usually a product of human activities, D is probably correct. I wouldn't pick C because there is nothing about discussion between scientists.

[hfk]

D for 50 absolutely because of "first law, air purification scheme, ..."

[John750]

Hi FinMaster and hfk,

You guys are great, D is correct for question 50.

Thanks!