题目

将a mol Na和amolAl一同投入m g足量水中，所得溶液密度为dg·㎝－3，该溶液的质量分数为   （    ）A．82a /（46a + m）%                   B．82a /（69a + 2m）%C．8200a /（46a + m）%                 D．8200a /（69a +2 m）%  答案：C解析:略 根据所给情景选出最佳答案。当你想知道去邮局的路怎么走时，你会问：A. How can I get to the post office? B. How do you go to the post office? C. Can I go to the post office?