第4题: [单项选择]The key problem in dealing with returned plastic beverage containers is______. A. to sell them at a profitable price B. how to mm them into useful things C. how to reduce their recycling costs D. to lower the prices for used materials 参考答案:C 答案解析:[解析] 本题属细节性问题。我们读完第二和第三段以后发现,第三段中的第二句话就是有关垃圾处理中的问题,读完这句话后,我们对比四个选项发现,C选项how to reduce their recyclin