Steve Rowson is an engineer at Virginia Tech. In his lab, he tests how helmets hold up against different types of hits. No helmet can prevent concussions completely, says Rowson. But he's found that when wearing a newer football helmet, the player's head doesn't gain speed as much after a hit. That lowers the risk of concussions.

　　Many youth sports teams have set limits on physical contact to reduce the risk of concussions. In soccer, most concussions happen as a result of headers - shots or passes made with the head. That's why many people think kids shouldn't head the ball until high school.

　　These efforts should help, says Crutchfield. But the best way to prevent long­term brain injuries, he says, is to stop playing immediately if you suffer concussion. "Protect yourself today so you can play again tomorrow."

　　语篇解读：本文是一篇说明文。青少年在运动中因头部撞击导致脑震荡的比例在逐年增高，工程师、医生和教练正采取措施改善这一情况。

4．Concussions among young players ________.

　　A．are rare before 2002

　　B．seem extremely worrying

　　C．cause kids to lose interest in sports

　　D．are mostly caused by wearing no helmets

　　解析：选B　推理判断题。由第二段中的"more common"和"each year increased by 6 percent"可知，青少年因体育运动导致脑震荡的情况越来越严重，令人担忧。

5．The author mentions the sudden stop of the bus to ________.

　　A．stress it's dangerous to ride buses

　　B．show human brains are easily damaged

　　C．give a better explanation of concussions

　　D．remind people to wear helmets while playing sports

　　解析：选C　推理判断题。作者在第五段中提到公交车急刹车时人们会受到撞击，将之与人们在运动时发生脑震荡的情况相比较，使这一概念更容易被理解。

6．Dr. Crutchfield suggests that after receiving a concussion, young players should ________.

　　A．never head the ball

　　B．avoid dangerous sports

　　C．play other kinds of sports

　　D．stop playing the sport for a while

　　解析：选D　细节理解题。由最后一段中的"stop playing immediately if you suffer concussion"可知，Crutchfield建议年轻的运动员在运动中发生脑震荡时，一定要及时停止运动，这样才能避免给大脑造成长期的损伤，才有利于今后更好地进行这项运动。