[单项选择]

{{B}}TEXT A{{/B}}

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
A. scientific arguments
B. convincing testimony
C. common sense observations
D. analogy