位于某江下游的某大城市 ,决定整治该市所面临的水域污染。但是 ,由于其污染源并非完全来自本市 ,该江中上游的污水和废弃物不断顺流而下 ,这就明显地加大了整治的难度。道理非常简单 ,其源不清 ,其流难洁而已。同样或类似的情况 ,还表现于一人清扫、万人投污 ,或者除污者少、 A large city located in the lower reaches of a river decided to remediate water pollution in the city. However, due to its source of pollution is not entirely from the city, the upper reaches of the river sewage and waste continue downstream, which obviously increased the difficulty of remediation. The reason is very simple, its source is unclear, its flow is difficult. The same or similar circumstances, but also manifested in one person to clean up, polluting million people, or decontamination less,