A
Adolescents have always been known to do wild, even dangerous things.This was thought to be due to the foolishness of youth. Now, brainimaging technology allows scientists to study the physical development of the brain in more detail than ever before. Their discoveries have led to a new theory of why teens act this way.
Recently, scientists discovered that though our brains are almost at their full size by the age of six, they are far from fully developed. Only during adolescence do our brains truly grow up. During this time, they go through great changes, like a computer system being upgraded (升级)．This upgrade was once thought to be finished by about age 12. Now, scientists have concluded that our brains continue to change until age 25. Such changes make us better at balancing impulses (冲动). But a stilldeveloping brain does this awkwardly. The result, scientists say, is the unpredictable behavior seen in teenagers.
The studies find that teens are more likely to take risks. Fortunately, the news isn't all negative. As brain scientist B．J.Casey points out, the teen brain inspires such behavior in order to help teens prepare for adult life.
One way the brain does this is by changing the way teens measure risk and reward. Researchers found that when teens think about rewards, their brain gives off more of the chemicals that create pleasure than an adult brain would. Researchers believe this makes the rewards seem more important than the risks, and makes teens feel the excitement of new experiences more strongly than adults do.
Research into the teen brain also found that it makes social connections seem especially rewarding. So, it connects social rewards with even more pleasure. In this way, the brain encourages teens to have a wide circle of friends, which is believed to make us more successful in life.
Unfortunately, this hunt for greater rewards can sometimes lead teens to make bad decisions. However, it also means that teens are more likely, and less afraid, to try new things or to be independent. The scientists' findings suggest that in the long run, the impulses of the teen brain are what helps teens leave their parents' care and live their own lives successfully.
语篇解读：本文是说明文。文章介绍了新的科学发现——为何青少年易于表现出极端行为。
1．What did scientists find recently?
A．How teenagers' brains work.
B．Why teenagers behave in extreme ways.
C．When a teenager's brain is well developed.
D．Which part of the brain changes in adolescence.
解析：选B 细节理解题。根据首段中“Their discoveries have led to a new theory of why teens act this way”可知，科学家发现了导致青少年行为极端的原因。
2．What does the author mean by “the news isn't all negative” in Paragraph 3?
A．Teenagers deal with new things better than adults.
B．The way the teen brain works has some advantages.
C．The negative side of the research is not understood.
D．Teenagers are able to change their behavior gradually.
解析：选B 推理判断题。根据第三段中的“As brain scientist B．J.Casey points out, the teen brain inspires such behavior in order to help teens prepare for adult life”可知，青少年的这种大脑运行方式有其有利之处。
3．How does the teen brain differ from the adult brain?
A．Teens attach greater importance to risks than rewards.
B．Adults are more likely to connect risks and rewards.
C．Adults have stronger belief in themselves.
D．Teens get more pleasure from rewards.
解析：选D 细节理解题。根据第四段中的“Researchers found that when teens think about rewards, their brain gives off more of the chemicals that create pleasure than an adult brain would”可知，青少年会从奖赏中感受到比成年人更多的快乐。
