C．They slow down the players' running speed.

　　D．They allow the players to move their heads more freely.

　　解析：　细节理解题。由倒数第三段中的 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可知，新款头盔效果更好些，可以更好地保护运动员的头部免受伤害。

　　答案：　B

　　7．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：　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开展这项运动。

　　答案：　D

　　C

　　New research from the University of Miami is showing that languages with complex tones- like Mandarin-tend to occur more often in wet regions，while languages with simple tones-like Swedish-occur in dry regions.

　　"English is a non­tonal language which originates in a relatively dry part of the world.It's in the top 15 percent of the 'driest' languages.This fits with our hypothesis (假说)．It's perfectly possible that the English language could adopt tones in areas that are now more humid，or as the climate changes，" says Sean Roberts，who works on global differences in geophonetics (地理语音学)．The research changes how language evolution is understood，with data drawn from over half the world's tongues."Broadly，this suggests another non­conscious way in which humans have adapted to their very different and extremely cruel environments，" says Caleb Everett，the researcher on the project."Also，there may be some health benefits to certain sound patterns in certain climates，but more research is needed."Breathing in dry air may cause a speaker's voice box to lose too much water，decreasing voice range.

"There's a hypothesis several anthropologists，who study people，society and culture，have put forward that languages in warmer climates such as Kenya tend to have higher rates of mouth opening，" says Everett.