第15题: [单项选择]He found it necessary for us ______ from each other. A. to help and learn B. helping and learning C. to learn and help D. learning and helping 参考答案:A 答案解析:[分析] 句意:他觉得我们彼此相互帮助和学习很有必要。本题考查句式结构。find it necessary for sb.to do sth.的意思是“发现某人必须做某事”。