题目

阅读理解。根据短文内容,选择正确答案。Life in the twenty-first century will be very different from life today. Between then and now many changes will take place, but what will the changes be?The population is growing fast. There will be many people in the world and most of them will live longer than people live now.Computers will be much smaller and more useful, and there will be at least one in every home. And computer studies will be one of the important subjects in schools then.People will work fewer hours than they do now and they will have more free time for sports, watch下列五种气体：氢气、甲烷、一氧化碳、二氧化碳、氧气．用化学式填写：有剧毒的是 ；理想的无污染能源是 ；能使带火星木条复燃的是 ；能在空气中燃烧生成两种物质的气体是 ．