What new research reveals about the adolescent brain. We 're learning that the teen years are a period of crucial brain development subject to a host of environmental and genetic factors. This emerging research shed light on a discovery that our brains are not finished maturing by adolescence, brains are only about 80 percent of the way to maturity, it takes until the mid-20s, and possibly later, for a brain to become fully developed. An excess of gray matter (the stuff that does the processing) at the beginning of adolescence makes us particularly brilliant at learning, but also particularly sensitive to the influences of our environment. Our brains' processing centers haven't been fully linked yet, particularly the parts responsible for helping to check our impulses and considering the long-term repercussions of our actions. It' s partially because of this developmental timeline that a teen can be so quick to think a harsh remark, or a biting insult, and so uninhibited in firing it off at the nearest unfortunate target. Instead, the full developed brain regions of an adult might stop himself from saying something cruel. In a paper published last year, Dr. Jay Giedd, wrote that, gray-matter (the stuff that does the processing) volume peaks around or just before the beginning of puberty, and then continuously declines. In contrast, white matter (the stuff that helps connect areas of the brain) increases right up to, and beyond, the end of puberty. These adolescent brain developments don't happen to all parts of the brain at the same time. "The order in which this maturation of connection goes, is from the back of the brain to the front of the brain," says Jensen. And one of the last parts to mature is the frontal lobe, a large area responsible for moderating reward, planning, impulsiveness, attention, acceptable social behavior, and other roles that are known as executive functions. Unfortunately, it' s just these sorts of behaviors that teenage brains are not fully endowed to deal with—and the consequences are potentially fatal when it comes to high-risk behavior like drinking and driving. This blast of teen-brain change is compounded by profound social and psychological shifts. Of particular importance is that adolescence is the time when we develop stronger social connections with our peers. Healthy social relationships have a positive effect on how an adolescent navigates through a tumultuous period of life. But at the same time, this reliance on friends makes young people susceptible to the influence of peer pressure, even when it is indirect.

单选题 One of the most important discoveries in the adolescent brain is that______.

【正确答案】 D

【答案解析】解析：根据题干关键词定位到文章第一段。该段最后一句指出“最新研究发现少年的大脑只有80％是成熟的”，其完全的成熟应该在20岁中期，或者更晚才能完成，故D项“在二十五岁前不成熟”是对原文的同义转换。B项“受到环境和遗传因素的影响”，原文中提到受到环境和基因因素影响的是大脑的发展，并不是对有关青少年大脑的探讨。A项“充分发展”和C项“对我们的环境敏感”均不符合题意，故选D。

单选题 Teenagers are more likely to______.

【正确答案】 A

【答案解析】解析：根据题干关键词定位到文章第二、三段。文章第三段指出a teen can be so quick to think a harsh remark，or a biting insult，and so uninhibited in firing it off at the nearest unfortunate target，即“青少年容易向最亲近的人发火，不能像成年人那样控制自己的情绪”，故A项“伤害最亲近的人”正确。B项“避免说一些残忍的话”与原文意思相反。C项“对他们的环境漠不关心”和D项“迷惑他们的父母”在原文中并未提及，故选A。

单选题 Which of the following statement is NOT correct?

【正确答案】 D

【答案解析】解析：题干中没有关键词，这类细节题需要通过选项中的具体信息进行定位。根据 gray-matter(the stuff that does the processing)volume peaks around or just before the beginning of puberty和white matter(the stuff that helps connect areas of the brain)increases right up to， and beyond，the end of puberty可知，大脑灰质在青春期左右达到峰值，主要负责处理信息。大脑白质在青春期之后会逐渐增多，主要司管人类脑部建立联系的能力，所以D项“白质可能会在青春期后减少”错误。A项“白质可以帮助连接大脑的不同部位”、B项“大脑成熟的顺序是从后到前的”和C项“灰质的体积将在青春期开始的时候达到峰值”原文中均有提及，故选D。