2. 外语
  3. Why is it so difficult to fall asleep when you are overtired? There is no one answer that【C1】______ to every individual. But man

Why is it so difficult to fall asleep when you are overtired? There is no one answer that【C1】______ to every individual. But man

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问题     Why is it so difficult to fall asleep when you are overtired? There is no one answer that【C1】______ to every individual. But many people fail to note the【C2】______ between fatigue — physical tiredness — and sleepiness, the inability to【C3】______ awake. It is possible to feel tired【C4】______ and still be unable to fall asleep, because while your body may be exhausted, you don’t feel【C5】______. To fall asleep, you need adequate time to unwind,【C6】______ you feel fatigued, not so easy to【C7】______ "turn off."
    According to Carl E. Hunt, director of the National Center on Sleep Disorders Research in Bethesda, Maryland, most people do not allow themselves【C8】_____ deceleration.
    Lack of sleep【C9】______ matters even more. Experts say adults need at least 7 to 8 hours of sleep a night to【C10】______ properly. When you get less sleep than【C11】______ on consecutive nights, you begin to accrue "sleep debt".【C12】______ sleep debt increases and functionality decreases, your body experiences a stress response and begins to release adrenaline. Now a vicious【C13】______ has been created: You experience the feeling of being more and more tired,【C14】______ your body is increasingly stimulated. Power sleeping for more hours on weekends is only a【C15】______ solution. "There is no【C16】______ for getting a good night’s sleep on a【C17】______ basis," says Hunt.
    Most of us,【C18】______, don’t get the sleep we need. According to the 2002 National Sleep Foundation, Americans sleep a(n)【C19】______ of 6.9 hours per night during the week, and 58 percent of adults experience【C20】______ of insomnia a few nights a week or more.
【C13】
选项 A、period
B、cycle
C、time
D、round
答案B
解析 语义线索题。下文冒号后的句子中more and more．．．increasingly说明此处指形成了一个循环，故B项cycle“周期，循环”正确。period表示“一段时间”；time表示“时间”；round表示“圆，圆形物”。
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