题目

In Switzerland, people ________ visit a friend’s house.        A. make plans      B. make plans to   C. makes plans to  D. make a plant 答案：B由苯乙烯和乙醛组成的混合气体，经测定：碳元素的质量分数为72%，则混合物中氧元素的质量分数为                                                （    ）   A．22%             B．32%              C．2%             D．19.56%