题目

Many people say that they are working too many hours. They don’t have enough time to relax or stay with their family. Work hours are different from one country to another. In France, people spend about 1646 hours a year at work. In Japan, however, people work about 2159 hours a year. That means a Japanese worker works 513 more hours a year than a French worker.    Why do people work so many hours? Some people work extra hours because they want to make more money. However, many companies don’t pay overtime. Their workers don’t get more pay for more work. These people think iX，Y，Z三种气体，把a molX和b molY充入一密闭容器中，发生反应：X＋2Y2Z达到平衡时，若它们的物质的量满足：n（X）＋n（Y）＝n（Z），则Y的转化率为（　） A．　　　　　　　 B． C．　　　　　　D．