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  Your teenage son looks like a grown man. He’s inches taller than his father, and his voice has turned deep. But his behavior is another matter. He makes hasty  decisions, drives cars too fast and tends to make his parents annoyed.

That’s because his brain is developing more slowly than the rest of his body. Researchers at the National Institute of Mental Health and UCLA conducted a decade-long study of normal brain development. They found that the frontal lobe, the area responsible for understanding future consequences, making wise decisions and  controlling impulses（冲动）, has not become mature （成熟的）until the early 20s.

Immature brains have fast-growing synapses （突触）and sections that remain unconnected. As a result, they're easily influenced by the environment and susceptible to unexpected behavior.

 This may explain the puzzling contradiction of adolescence. Teens are at their physical prime. Yet their death rates rise sharply. Study shows that rates of  death by injury for people between the ages of 15 and 19 are six times those seen in kids ages 10 to 14. The Insurance Institute for Highway Safety reports that teens  are four times more likely than older drivers to be involved in a car crash and three times more likely to die in one. 

Adolescents also are more susceptible to the effects of drugs and alcohol. Rates of drug and alcohol abuse are high when compared with other age groups. Frances  Jensen and David Urion, doctors at Children’s Hospital Boston and Harvard Medical School, discovered that adult brain cells recovered more quickly from alcohol  exposure than younger brain cells. Jensen said in Harvard Magazine: “For a teenager, what he drank on the weekend is still with him during that test on Thursday.”

The implications for parents are clear. Teens aren’t making trouble on purpose. They desire independence, but they are still tender. They’re still  forming into the adults they’ll eventually be. And, of course, they won’t be this age forever. Finally, they will grow up and become rational and wise adults.

1.Which of the following is NOT the typical behavior of a teenage boy?

A Driving speeding cars.

B Offending their parents.

C Following parents’ advice.

D Making careless decisions.

解析：选C。细节理解题。根据第一段第四句He makes hasty decisions, drives cars too fast and tends to make his parents annoyed可知处于青春期的男孩行事草率、开车超速、冒犯父母。C项没有提及，故选C项。

2.A teenager’s frontal lobe probably doesn’t reach maturity until he is about_____.

A 15 years old

B 18 years old

C 22 years old

D 28 years old

解析：选C。细节理解题。根据第二段最后一句The frontal lobe, the area responsible for understanding future consequences, making wise decisions and controlling impulses（冲动）, has not become mature （成熟的）until the early 20s可知青少年的大脑额叶要到20出头的时候才会成熟。

3.Teens’ death rates rise sharply because of their _______.

A immature brains

B faulty frontal lobes

C fast-growing cars

D changeable environments

解析：选A。细节理解题。根据第三段第一句Immature brains have fast-growing synapses（突触） and sections that remain unconnected及第四段第一句This may explain the puzzling contradiction of adolescence可知少年死亡率较高的根本原因是少年的大脑发育还不成熟。

4.From the last paragraph, we can make a conclusion that______.

A teenagers should have freedom to do what they like to do

B teenagers still need lots of supervision from caring parents

C teenagers tend to make their parents annoyed on purpose

D teenagers can make wise decisions and control impulses

解析：选B。推理判断题。根据最后一段第三句They desire independence, but they are still tender可知青少年虽然渴望自由，但他们还太嫩。故可判断他们仍然需要父母的呵护和监管。