题目内容：

It’s nearly noon on a Saturday and you can’t believe it: your teenager is still in bed, sleeping away. But before you wake him up---mumbling to yourself that you can’t believe what a lazybones he is---you should know that he probably needs all the zzzs he can get.

As much as nine hours of sleep a night, in fact. Furthermore, teens’ circadian rhythms (i.e., processes that occur once a day) mean that young people would rather stay up past midnight and rise after 9 a.m. The result? Many teens stay up late, drag themselves out of bed early for school and try to make up the sleep debt on the weekends---or in class!

“There’s a biological reason why teens stay up late and want to sleep late,” says Dr. Stan Kutcher, the Sun Life Chair of Adolescent Mental Health at Dalhousie University in Halifax. “Their natural sleep-wake cycle changes as part of the maturation process. And because of changes in their social activities, recovering from sleep debt is more problematic.”

Teens need extra sleep for several reasons. First, their brains are changing. “The brain is reorganizing itself, laying down new pathways. What we’re seeing is a relationship between brain redevelopment and an increased need for sleep,” says Kutcher. As well, growth hormones are released during sleep, so adequate sleep is crucial for adolescents’ physical development. In addition, everything adolescents have learned in school that day is being processed and locked into long-term memory during sleep. Sufficient sleep also plays a key role in overall physical health. The immune system, for example, needs deep sleep to become and remain robust(healthy).

Staying up late on school nights means that, on average, teens get between six and a half and seven hours of sleep a night---about two hours less than they need. As a result, many either doze off in class or have trouble concentrating. Some of the behavioural problems and irritability in teens can be linked directly to sleep deprivation(损失), Kutcher says.

Then there’s the breakfast issue. Dr. Carlyle Smith, a sleep researcher and a psychology professor at Trent University in Peterborough, Ont., adds that many teens simply cannot tolerate food when they first wake up, so skipping breakfast becomes another factor in reduced alertness in class. The most obvious solution to the teen sleep problem is to have school start later in the day, but initiatives(积极性) toward this across the country have gone nowhere, Smith says, mainly because of costs and resistance from school boards and teachers.

So for now, just sympathize with your teens. Encourage them to go to bed, if not early, then at least at a regular time, so they won’t develop insomnia from erratic(不稳定的) schedules. Warn them not to have too many caffeinated drinks before bed. And don’t let sleeping away the weekend become an issue to fight over. Schedule family activities to take place later in the day on weekends and let them sleep in. “If you want your kids to grow and remember stuff, let them sleep,” says Smith. “It’s not laziness. Their brains are working really, really hard.”

1.The word “zzzs” (Paragraph 1) most probably means __________.

A．food             B．sleep             C．energy           D．blame

2.What causes teenagers to be less sleepy late at night and more sleepy early in the morning?

A．Caffeinated drinks.

B．Too much family activities.

C．Circadian rhythms.

D．Too much homework.

3.How many reason why teens need extra sleep are mentioned in Paragraph 4?

A．Three.            B．Four.             C．Five.             D．Six.

4.One of the reasons why many teenagers fail to have better performances in class is that __________.

A．teenagers go to bed early and sleep late

B．teenagers stay up late and get up late

C．teenagers participate in too many social activities at night

D．teenagers skip breakfast because of sleeping in

5.The author wrote this article to __________.

A．advise parents to let sleeping teenagers lie

B．explain why teenagers often sleep late

C．state schools should start late in the day

D．warn teenagers not to drink coffee before bed