题目

Ask any American what he/she is doing on Sunday, February 7 and the answer is likely to be either hosting or attending a Super Bowl Party. Played for the title of the National Football League Champion, Super Bowl is the most watched annual television program in the United States. That's because Super Bowl which is celebrating its Golden Anniversary this year, is more than just a 60-minute football game—it is a well-designed production that features half-time performances, fireworks shows and television ads that people discuss for days. But most important of all, it is the day to set15．R1河段与R2河段比较，R1河段（　　）A．含沙量大B．冰期长C．流量大D．无污染