We felt amazed at the use the waste bottles.
A. they had made
B. they had made of
C. they had put
D. they had put to
网友回答
A. they had made
(答案→)B. they had made of
C. they had put
D. they had put to
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”。