题目

Once a farmer lost his watch in his barn, in which lots of grain was kept. The watch,    61    was a gift from his father, was very important to him and he was determined to find it. After searching the barn for a long time, however, he gave up and asked for help from a group of children who were playing nearby. He promised to give a great reward to    62    found the watch.    63   (hear) this, the children hurried inside the barn immediately.    64    searched everywhere but still could not find the watch buried in the grain. The farmer was about to give up  65�下面是美国的北水南调和澳大利亚的东水西调示意图及相关资料介绍，图中箭头表示 调水方向，据图和资料分析回答下列问题。材料一 美国太平洋沿岸北部水资源丰富，但光热资源不足；南部光热资源丰富，但水资源缺乏。由于南部城市和人口多，所以对农产品的需求量大。为满足需求，美国将 北部的水引到南部，灌溉农田，发展亚热带水果、蔬菜和粮食的种植，使农产品不仅满足 了南部的需求，而且还能向北部输出。材料二 澳大利亚东南部的墨累—达令河流域是世界著名的混合农业区。随着农业 的发展，水资源缺乏现象越来越严重。为了保证区域经济的可持续发展，不得不从大分水 岭东部向西部引水，以解决农业灌溉的用水问题。(1) 为什么美国太平洋沿岸北部水资源有余，南部水资源缺乏?(2) 从工程建设的角度看，美国的北水南调和澳大利亚的东水西调，哪个难度大、投资高? 理由是什么?(3)澳大利亚东水西调实施后，东部调出区的河流中下游出现水质变差、污染加重的现 象，西部调入区出现土壤盐碱化加重的现象。请分析这两种现象产生的原因，并提出 防治西部调入区土壤盐碱化的措施。