This productivity, however, has its price. Intensive cultivation exposes theearth to the damaging forces ofnature. Every year wind and water remove tons ofrich soil from the nation's croplands, with the result that soil erosion has become anational problem concerning everyone from the farmer to the consumer. Each field is covered by a limited amount of topsoil, the upper layer ofearth which is richest in the nutrient and minerals necessary for growing crops. Inthe 1830s, nearly two feet of rich, black top soil covered the Midwest. Today theaverage depth is only eight inches, and every decade another inch is blown orwashed away. 48.（ A United States Agricultural Department survey states that iferosion continues at its present rate, corn and soybean yields in the Midwest maydrop as much as 30 percent over the next 50_years.）
【正确答案】：美国农业部的一份报告表明，如果土壤侵蚀以目前的速度继续下去的话，中西部地区玉米和大豆的产量或许会在未来的50年中下降多达30%。
【题目解析】：括号部分是一个复杂句，主语关键词是survey（调查），谓语是state（声明），宾语是that引导的宾语从句，其中包含if引导的条件状语从句，该从句的主语erosion（土壤侵蚀）意思可以通过上下文线索判断出来。宾语从句的主语关键词是yields（产量），谓语是drop（下降），as much as引导了状语。一般在处理带有较长从句的句子时，常常采用破句翻译的方式，也就是说，把各个从句单独翻译，然后再整合到句中，在照顾句子逻辑关系的前提下译出符合中文表达习惯的译文。