一、拓展中线方案的背景与缘由目前多数人认为南水北调东中西三条线路各有各的供水范围 ,不能相互代替。但从我国实际情况出发 ,既不可能也不需要三条调水线路同时动工建设 ,必须按轻重缓急原则逐步实施 ,９０年代末期国家主管部门通过多方论证 ,首肯中线方案宜先走一步。主要 I. Background and Reasons for Expanding the Midline Program At present, most people think that the scope of water supply for each of the three routes in the east, the west and the south of the South-to-North Water Diversion Project can not be replaced by each other. However, proceeding from the actual situation in our country, it is neither possible nor necessary to start the construction of the three water transfer lines and must be implemented gradually according to the principle of priority. In the late 1990s, the competent national authorities passed the multi-factorial demonstration and should approve the middle-line proposal one step ahead. main