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  3. Municipal sewage is of relative]y recent origin as a pollutant. It was firs

Municipal sewage is of relative]y recent origin as a pollutant. It was firs

游客2023-11-20  38
问题      Municipal sewage is of relative]y recent origin as a pollutant. It was first brought to public attention in the 19th century by a London physician who showed that the city’s cholera outbreak had been caused by just one contaminated well. Even though the contamination of drinking water by disease germs has been nearly eliminated in this country, hundreds of communities are still discharging raw sewage into streams and rivers.
     When we consider that this sewage contains effluents from toilets, hospitals, laundries, industrial plants, etc. , then the potential of the pollutants as a health hazard is apparent.
     The problem of municipal sewage disposal is complicated by the fact that, years ago, most cities combined their storm and waste disposal sewers. Many of these combined systems work well, but others cannot cope with sudden heavy rains. When such storms occur, water mixed with sewage may flood and disable treatment plants unless bypassed, untreated, into a stream. In either case; the people may have little protection for several days from these wastes that may contain disease germs.
     Even if adequately treated to eliminate the health hazard, sewage is aesthetically undesirable because of odors and colors produced. Detergents have posed a particular disposal problem. Although there is no indication that they are injurious to health, they can cause foaming, which can clog treatment plants and, at the least, spoil the scenic beauty of streams.
     Rural and suburban residents should be aware that septic tanks and cesspools are a potential source of pollution to ground water supplies. This is especially true in the suburban areas with a high population density and with
no municipal sewage disposal and treatment system available. In some areas, sewage disposal is accomplished by cesspools. Soil research is furnishing guidelines for more effective and safer use of systems such as these. [br] The author mentions the London cholera epidemic to ______.
选项 A、prove that the city refused to deal with pollution
B、prove that medical science once knew little about pollution
C、introduce the idea of contaminated water supplies
D、recall a historical fact
答案 C
解析 此题为细节题。答案在第一段。线索词为“London cholera”。此题考查作者引用的目的。A项与文中所述事实相反。B项文中未涉及此话题。D项“London cholera”是一个“historical fact”，却不是作者引用之目的。
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