题目

I tend to accept any idea put forward by experts on TV. One day, a sociologist proposed（提出，建议） that the    16    society has been consuming (消费）modern humans little by little. For fear that I would become a victim（受害者）of the consumer society, I   17  hurried to a bicycle shop in my neighborhood.   18  the shopkeeper Mr. Johnson was selling me the bicycle, he said, “This is the best thing you   19  have done. Life has become hopelessly   20  . A bicycle is simple, and it brings to you   21  things: fresh air, sunshine and exercise.等差数列中，，记，则当____时， 取得最大值.