单选题 阅读理解 Passage 2 The biggest soccer organization in the U.S. introduces new rules to make the sport safer. The U.S. Soccer Federation announced that players in its teams who are 10 or younger are no longer allowed to head the ball. Players aged from 11 to 13 have limits on how often they can practice heading. The new rules are set to stop kids from getting hurt because of a blow to the head that shakes the brain. Players may get headaches by heading the ball. Even worse, they may also get concussions, which will cause lasting brain damage. Heading the ball can be one of the most dangerous parts of soccer. Sometimes the force of hitting the ball with their heads gives players concussions. But more often, players receive concussions when they jump to head the ball and by accident knock heads with other players or fall and hit their heads on the grass. "More concussions happen during the act of heading than any other action in soccer," says Dr. Robert Cantu, an expert on brain damage. So far, the new rules are only used by teams that are part of the U.S. Soccer Federation. But the group says it hopes more soccer teams will soon follow its example. Former U.S. soccer star Brandi Chastain is one of the leaders of the activity to ban heading among young soccer players. She welcomes the rule change but wants the rule to include all players under 14小题:What's the main idea of the passage? ( )