Municipal sewage is of relatively 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, mostcities 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.

　　1. This passage is concerned primarily with the _____ .
　　A. problems of waste disposal
　　B. dangers of drinking from wells
　　C. turbidity of polluted water
　　D. outbreak of cholera

　　2. The author mentions the London cholera epidemic to _____ .
　　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

　　3. In densely populated suburban areas, a danger exits from _____ .
　　A. streams that do not flow directly to open bodies of water
　　B. cesspools and septic tanks that contaminate water supplies
　　C. storm and waste disposal sewers that have been combined
　　D. the undesirable odors of sewage

　　4. In developing the main point, the author makes use of _____ .
　　A. scientific arguments
　　B. convincing testimony
　　C. common sense observations
　　D. analogy

　　答案：ACBC