2. 外语
  3. A. arbitrary B. avoided C. complicates D. created E. distinctions F. each G. features H. individual I. rar

A. arbitrary B. avoided C. complicates D. created E. distinctions F. each G. features H. individual I. rar

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问题    A. arbitrary   B. avoided    C. complicates   D. created    E. distinctions
   F. each     G. features    H. individual   I. rarely     J. simply
   K. substitute   L. sufficient    M. symptoms   N. temporary   O. that
   Why is it so difficult to fall asleep when you are overtired? There is no one answer that applies to every 【C1】______. But many people fail to note the 【C2】______ between fatigue—physical tiredness—and sleepiness, the inability to stay awake. It is possible to feel tired physically and still be unable to fall asleep, because while your body may be exhausted, you don’t feel sleepy. To fall asleep, you need adequate time to unwind, even if you feel fatigued, not so easy to 【C3】______ "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 【C4】______ deceleration (放慢).
   Lack of sleep 【C5】______ the matter even more. Experts say adults need at least 7 to 8 hours of sleep a night to function properly. When you get less sleep than 【C6】______ on consecutive nights, you begin to pile up "sleep debt". As sleep debt increases and functionality decreases, your body experiences a stress response and begins to release adrenaline. Now a vicious cycle has been  【C7】______: You experience the feeling of being more and more tired, but your body is increasingly stimulated. Power sleeping for more hours on weekends is only a 【C8】______ solution. "There is no  【C9】______ for getting a good night’s sleep on a habitual basis," says Hunt.
   Most of us, however, don’t get the sleep we need. According to the National Sleep Foundation, Americans sleep an average of 6.9 hours per night during the week, and 58 percent of adults experience 【C10】______ of insomnia a few nights a week or more.
【C9】
选项
答案K
解析 There be句型缺少主语。再结合句中的is可知，空格处应填入单数名词或不可数名词。substitute“代替品”代入句子，意为“养成规律的每晚睡个好觉的习惯是不可代替的”，句意通顺，故选K。
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