Having a teenager at home can be a real headache. Many teenagers smoke, drink and even fight. They often do something dangerous.

    Earlier studies have shown that teenagers are more likely (可能) to make irrational decisions than people from any other age group, including children and adults. Is it that teenagers are too young to tell right from wrong? Not really. So what's the reason?

    According to Laurence, a teacher from a US university, the reason is that teenagers care a lot about how their peers (同龄人) view them—that is “peer influence”.

    As children enter their teenage years, they spend more time with their friends and classmates, and also they care more about what they think of them. This makes teenagers make decisions without thinking about the costs.

    In a test, a group of teenagers were asked to play a video driving game. When they played with their friends watching around them, they took more chances and drove more carelessly because that would increase their possibility of winning. But when they played alone, they drove more safely.

    Why do peers have such a big influence on teens' behavior?

As Laurence sees it, a teenager's brain is like a car with a good accelerator (油门) but a weak brake (刹车). The “accelerator” is fully developed by teenage years while the “brake” is still not fully developed. When teenagers are watched by their peers, they usually push hard on the accelerator. With their weak brake, it is likely that they are going to end up in an accident.

    But the good news is that a violent (暴力的)teenager doesn't necessarily become a violent adult. About two-thirds to three-quarters of violent youth grow out of it. “They get more self-controlled.”

She drank and smoked ____ (heavy) for years.

由于许多地方大片植物被破坏，带来沙尘暴和洪涝灾害，这给我们的启示是（    ）

①不能去改造自然界                      ②不能破坏环境

③要爱护地球上的其他生物          ④要保护地球