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  3. One fact was clearly demonstrated by the early sleep researchers: one part of the night is not just like another. As scientists

One fact was clearly demonstrated by the early sleep researchers: one part of the night is not just like another. As scientists

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问题       One fact was clearly demonstrated by the early sleep researchers: one part of the night is not just like another. As scientists began to compare the records of volunteers during the 1950s, they observed that human sleep follows a rhythmic schedule. They noted that not only was this schedule much the same in healthy persons of the same age with similar habits but, from night to night, each individual had an EEG record almost as consistent as a signature.
      Sleep and wakefulness, once considered to be the light and dark of consciousness, no longer seem to differ so sharply. To sleep does not mean to drown in an ocean of darkness. Actually, sleep is not a unitary state; it involves many shades or degree of detachment from the surrounding world. While sleep may feel like a blanket of darkness punctuated by dreams—a time when the mind is asleep—nothing could be less true. All night long a person drifts down and up through different levels of consciousness, as if on waves. With laboratory methods, researchers have been able to chart the typical stages of the journey into sleep.
      The journey starts while the subject is still awake but beginning to relax. His brain waves, which have been low, rapid, and irregular, begin to show a new pattern. This new pattern, which is known as alpha rhythm, is an even electrical pulsation of about nine to 12 cycles per second. Most people do not know what the alpha state feels like, but during the last few years researchers have been able to teach subjects how to recognize and control their alpha rhythm.
     When their EEG shows an alpha rhythm, the subjects are notified, either by a sound or by the appearance of a color on a screen. Because the alpha state tends to be pleasant and relaxed, the ability to sustain it can help tense people ease their passage into sleep. A moment of tension, a loud noise, an attempt to solve a problem, however, and the alpha rhythm may vanish.
     As the subject passes through the gates of the unconsciousness, his alpha waves grow smaller, and his eyes roll very slowly. For a moment, he may wake up during this early part of the descent, alerted by a sudden spasm that causes his body to jerk. Like the brain waves, this spasm is a sign of neural changes within. Known as the myoclonic jerk, it is caused by a brief burst of activity in the brain. Although it is related to epileptic seizures, the myoclonic jerk is normal in all human sleep. It is gone in a fraction of a second, after which descent continues. The subject has not felt the peculiar transformation, but now he is said to be truly asleep.
This passage states that a person is really asleep only
选项 A、after dreaming has passed.
B、when his EEG reveals no alpha rhythm.
C、when his EEG begins to show an alpha rhythm.
D、after the completion of his alpha rhythm decline.
答案D
解析 本题考查推理判断。该题询问人真正进入睡眠状态是在什么时候。文章先是对人的睡眠进行浅析，而后对进入自然睡眠的过程进行如实描述，而真正进入睡眠状态是该过程所要达到的一个最终状态，所以答案应在文章末尾。文章的第三段开始讲述人在处于彻底放松，将要入睡时，他的脑电波就会出现“alpha rhythm”，而且随着人的意识逐渐模糊，“alpha rhythm”的强度会不断削弱，直到文章最后一段的最后两行所描述的“It is gone in a fraction of a second，after which descent continues．The subject has not felt the peculiar transformation，but now he is said to be truly asleep．”在人进入熟睡的过程中会伴有瞬间的抽动，这之后“alpha rhythm”继续减弱直到完全消失，这时人才真正进入到无意识的熟睡状态。句中“descent continues”是指“alpha rhythm’s descent continues”。因此人进入真正的睡眠状态是在“alpha rhythm”完全消失以后。
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