Section   B

Getting lesss leep has become a bad habit for most American kids. According to a new survey(调查) by the National SleepFoundation, 51% of kids aged 10 to 18 go to bed at 10 pm or later on schoolnights, even though they have to get up early. Last year the Foundationreported that nearly 60% of 7- to 12-year-olds said that they felt tired duringthe day, and 15% said they had fallen asleep at school.

How much sleepyou need depends a lot on your age. Babies need a lot of rest: most of themsleep about 18 hours a day! Adults need about eight hours. For most school-agechildren, ten hours is ideal(理想的). But the new National Sleep Foundation survey found that35% of 10- to 12-year-olds get only seven or eight hours. And guess what almosthalf of the surveyed kids said they do before bedtime? Watch TV.

“More childrenare going to bed with TVs on, and there are more opportunities(机会) to stay awake, with morehomework, the Internet and the phone,” says Dr. Mary Carskadon, a sleepresearcher at Brown University Medical School. She says these activities atbedtime can get kids all excited and make it hard for them to calm down andsleep. Other experts say part of the problem is chemical. Changing levels of bodychemicals called hormones not only make teenagers’ bodies develop adult zxxk characteristics,but also make it hard for teenagers to fall asleep before 11 pm.

Because sleepiness is such a problem for teenagers,some  school districts have decided to start high school classes later thanthey used to. Three years ago, schools in Edina, Minnesota, changed the starttime from 7:25 am to 8:30 am. Students, parents and teachers are pleased withthe results.

What is the new National Sleep Foundation surveyon?

How many hours of sleep do 11-year-olds need every day?

Why do teenagers go to sleep late according to Carskadon?