题目

He is believed____________ in at his office on his way home.   A. dropping                     B. to have dropped   C. having dropped               D. to be dropped 答案：B 解析: 首先be belived to do是固定用法；drop in at接地点表示拜访某地。H2还原CuO的操作步骤有：①加热 ②通氢气③停止通氢气④停止加热，正确的操作顺序是（ ）A．①②③④B．②①④③C．①③②④D．②①③④