THE ASEAN PARA-GAMES ARE HOSTED BY THE SAME COUNTRY WHERE THE SEA GAM...

Câu 44: The ASEAN Para-Games are hosted by the same country where the SEA Games took place.

A defended B impressed C participated D organized

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 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 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 a region,

human output may be dominant and may temporarily overload the natural purification scheme of the

cycles. 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, has a natural level of 0.1 ppm and is not usually a pollutant until its level reaches about 15 ppm.