[单项选择]

All we have a clock located inside our brains. Similar to your bedside alarm clock, your internal clock runs on a 24-hour cycle. This cycle, called a circadian rhythm, helps control when you wake, when you eat and when you sleep.
Somewhere around puberty, something happens in the timing of the biological clock. The clock pushes forward, so adolescents and teenagers are unable to fall asleep as early as they used to. When your mother tells you it’s time for bed, your body may be pushing you to stay up for several hours more. And the light coming from your computer screen or TV could be pushing you to stay up even later.
This shift is natural for teenagers. But staying up very late and sleeping late can get your body’s clock out of sync with the cycle of light and dark. It can also make it hard to get out of bed in the morning and may bring other problems, too. Teenagers are put in a kind of a gray cloud when they don’t get enough sleep, says Mary
A. Our biological clock resets itself automatically.
B. Light gets through our eyes and resets our biological clock.
C. Our internal clock as well as the alarm clock can be reset automatically.
D. Our internal clock, like the alarm clock, can be reset.