单选题We felt amazed at th

问题补充：

单选题Wefeltamazedattheusethewastebottles.A.they had madeB.they had made ofC.they had putD.they had put to

答案：

B解析本题使用make use of短语的被动形式，先行词use在定语从句中作made的宾语，句意为“我们对他们对废酒瓶的利用感到吃惊”。