2. 外语
  3. When a person falls asleep, all activity decreases and the muscles relax. The heartbeat and breathing【C1】______slow down. The pe

When a person falls asleep, all activity decreases and the muscles relax. The heartbeat and breathing【C1】______slow down. The pe

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问题     When a person falls asleep, all activity decreases and the muscles relax. The heartbeat and breathing【C1】______slow down. The person slowly becomes less aware【C2】______what may be happening all around. A sleeping person changes the【C3】______of the entire body at least a dozen times during about eight hours of sleep. The head, arms, or legs are moved more often.
    Scientists study sleep【C4】______an instrument. Whether a person is【C5】______or asleep, the brain gives【C6】______electrical waves. The instrument measures and records these waves. The brain of an awake, 【C7】______person gives off about 10 small waves a second. As a person falls deeply【C8】______sleep, the brain sends out slower but 【C9】______waves. The slowest, largest waves【C10】______during the first two or three hours of a period of sleep. During slow-wave sleep, mental activity【C11】______down but does not stop. Persons awakened【C12】______slow-wave sleep can often【C13】______unclear thoughts that they had while asleep. Periods of small, fast waves, 【C14】______to those of an awake person, occur at【C15】______during sleep. During these periods of fast brain wave activity, the sleeper’s eyes move rapidly as though they were watching the【C16】______of a dream. A sleeper who is awakened during such a period probably will recall dreaming and remember【C17】______of the dream. Sleep during these periods is called dreaming sleep or REM (Rapid Eye Movement) sleep. An eight-hour period of sleep includes from three to five periods of dreaming sleep. The dreaming sleep periods【C18】______from 5 to 30 minutes【C19】______and occur every 90 to 100 minutes. The【C20】______dream periods last longer than the earlier ones.
【C15】
选项 A、gaps
B、distance
C、length
D、intervals
答案D
解析 语义衔接题。四个选项中能与at连用的只有length和intervals，at length表示“最终”，与此处语义不符：at intervals表示“每隔一段时间”，符合此处语义，故答案为[D]intervals。
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大学英语四级

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