athletes to wear helmets.Helmets help reduce the force of a hit.The hard outer shell spreads the force over a larger area.Inside a helmet，a plastic or air­filled lining also helps soften the blow.

　　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、医生和教练采取措施改善这一情况。

　　4．Concussions among young players .

　　A．are rare before 2001

　　B．seem extremely worrying

　　C．cause kids to lose interest in sports

　　D．are mostly caused by wearing no helmets

　　解析：　推理判断题。由第二段中的more common和each year increased by 62 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。

　　答案：　B

　　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：　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。

　　答案：　C

　　6．What does Steve Rowson think of the newer football helmets?

　　A．They vary a lot in size.

B．They work better than the old ones.