Like an effluent charge system, a system of marketable permits would provide a continuous incentive to reduce pollution, since retained permits would tie up funds which could be freed by sale of unneeded permits for the going price.

• 正像污水排放收费制度一样，一种可出售的许可证制度就是提供一种持续的减少污染的鼓励，因为持有许可证就会占用资金，占用的资金又可通过出售没有必要的许可证而获得解脱。