Tham khảo tài liệu 'kỳ thi thử đại học lần i năm học: 2010 - 2011 môn thi: tiếng anh', tài liệu phổ thông, ôn thi đh-cđ phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | KỲ THI THỬ ĐẠI HỌC LẦN I NĂM HỌC 2010 - 2011 TRƯỜNG THPT QUANG TRUNG ĐỀ CHÍNH THỨC Môn thi TIẾNG ANH Đe thi có 06 trang Thời gian làm bài 90 phút Không kể thời gian giao đề Read the following passage and choose the correct answer. 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 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 are pollutants such as sulfur dioxides 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 is output of these compounds dwarfs resulting from human activities. However human production usually occurs in a localized area such as a city. In this localized 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 concentrations need not be large for a substance to be a pollutant in fact the numerical value
