2. 外语
  3. Our sleep time over the past century has been【B1】______ by almost 20 percent. Generally, adults need to sleep one hour for e

Our sleep time over the past century has been【B1】______ by almost 20 percent. Generally, adults need to sleep one hour for e

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问题     Our sleep time over the past century has been【B1】______ by almost 20 percent.
    Generally, adults need to sleep one hour for every two hours【B2】______ , which means that most need about eight hours of sleep a night. Of course, some people need more and some less. Children and teenagers need an average of about ten hours.
    The brain keeps an exact【B3】______ of how much sleep it is owed. My colleagues and I【B4】______ the term sleep debt because【B5】______ lost sleep is like a【B6】______ debt: it must be paid back. If you get an hour less than a full night’s sleep, you carry an hour of sleep debt into the next day and your  【B7】______ to fall asleep during the daytime becomes stronger.
    During a five-day【B8】______ , if you get six hours of sleep each night instead of the eight you needed,【B9】______ . Because sleep debt accumulates in an additive fashion,【B10】______ From this perspective, sleeping until noon on Saturday is not getting enough to pay back the ten lost hours as well as meet your nightly requirement of eight; you would have to sleep until about 5 p.m. to balance the sleep ledger.【B11】______ .
【B11】
选项
答案But for most people it is difficult to sleep that long because of the function of our biological clock
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