Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous changes. 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 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 more important air pollutants, such as sulfur oxides, carbon monoxides and nitrogen oxides are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. 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 from human activities.However, human production usually occurs in a localized area, such as a city. In such region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an 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 has a natural level of 0. 1 ppm and is not usually a pollutant until its level reaches about 15 ppm.
Câu 1: The word "detectable " is closest in meaning to .
A. special
B. separable
C. beneficial
D. measurable.
Câu 2: The word "localized " is closest in meaning to .
A. specified
B. circled
C. encircled
D. surrounded.
Câu 3: The word "these" in the second paragraph refers to .
A. the compounds moved to the water or soil
B. the various chemical reactions.
C. the pollutants from the developing Earth
D. the components in biogeochemical cycles.
Câu 4: 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 can be calculated quickly.
C. it is in a localized area
D. the natural level is also known.
Câu 5: It can be inferred from the first paragraph that .
A. the definition of air pollution will continue to change.
B. water vapor is an air pollutant in localized areas.
C. Most pollutants today can be seen or smelled.
D. a substance becomes an air pollutant only in cities.
Câu 6: According to the passage, human- generated air pollution in localized regions .
A. will react harmfully with natural pollutants.
B. can overwhelm the natural system removing pollutants.
C. will damage area outside of the localized regions.
D. can be dwarfed by nature's output of pollutants.
Câu 7: The word "adversely " is closest in meaning to .
A. considerably
B. quickly
C. admittedly
D. negatively.
Câu 8: Which of the following is best supported by the passage?
A. Scientists should be consulted in order to establish uniform limits for all air pollutants.
B. Human activities have been effective in reducing air pollution.
C. One of the most important steps in preserving natural lands is to better enforce air pollution laws.
D. To effectively control pollution, local government should regularly review their air pollution laws.
Câu 9: For which of the following reasons can natural pollutants play an important role in controlling air pollution?
A. They have existed since the Earth developed.
B. They occur in greater quantities than other pollutants.
C. They're less harmful to living beings than other pollutants.
D. They function as part of a purification process.
Câu 10: What does the passage mainly discuss?
A. The effects of compounds added to the atmosphere
B. The economic impact of air pollution.
C. What constitutes an air pollutant
D. How much harm air pollutants can cause.
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