A城市的郊区有一座水库,每年夏天都吸引大批游泳爱好者前去游泳。而水库是城市自来水工厂的重要取水源,为了保持水源的清洁卫生,自来水厂在库区竖了许多“禁止游泳”的牌子,但效果并不理想,人们照游泳不误。 A city has a reservoir in the suburbs, attracting a large number of swimming enthusiasts each summer to swim. However, the reservoir is an important source of water for urban tap water factories. In order to maintain the cleanliness of water sources, the water plant has set up a number of “no swimming” sign in the reservoir area, but the effect is not satisfactory.