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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.
According to the author, the alpha state has been shown to be
选项 A、immeasurable.
B、erratic in its rhythm.
C、a brief burst of activity in the brain.
D、controllable.
答案D
解析 本题考查细节理解。作者在第三段最后指出“during the last few years researchers have been able to teach subjects how to recognize and control their alpha rhythm．”研究人员已经能够教人们如何辨认并控制他们的“alpha rhythm”了，所以“alpha rhythm”是可控制的。选项 A 与文章内容不符，第四段第一句话表明“alpha rhythm”可以用声音或色彩来记录下来，因此不是“unmeasurable”；选项B 认为“alpha rhythm”是“erratic”(不稳定的)，而文章第三段指出“alpha rhythm”是“an even electrical pulsation of about nine to 12 cycles per second”平缓的有节奏的电波震动，每秒钟9到12次。由此可见，“alpha rhythm”具有很强的稳定性，所以应排除选项B ；选项C  a brief burst of activity in the brain在最后一段中是引起“myoclonic jerk”的原因，而且“It is gone in a fraction of a second”，而不是像“alpha rhythm”一样一直存在于人从放松到睡眠的过程中，所以不能被认为是“alpha rhythm”的表现形式。
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