So far, farmers have been able to compensate for the loss of fertile topsoilby applying more chemical fertilizers to their fields; however, while this practicehas increased crop yields, it has been devastating for ecology. 49.（ Agriculture hasbecome one of the biggest polluters of the nation's precious water supply. Rivers,lakes, and underground reserves of water are being filled in and poisoned by soiland chemicals carried by drainage from eroding fields. ）Furthermore, fertilizersonly replenish the soil; they do not prevent its loss.
【正确答案】：农业已经称为该国宝贵的水资源的最大污染源之一。河流、湖泊以及地下水中充斥着来自受侵蚀的农田排水所夹带的泥土和化学物质，并因此正在受到污染。
【题目解析】：括号部分是两个简单句。这两句的难点主要在词汇，如polluter（污染源，污染物）、water supply（水资源）、underground reserves of water（地下水）、drainage（排水）、eroding（正在受到侵蚀的）等。另外一个难点就是第二句的被动语态进行时 are being filled in and poisoned by中包含了两个动词，需要采取破句处理的方式分别译出。
