2001年1月大学英语六级考试真题试卷 - 阅读1
Passage One Questions 11 to 15 are based on the following passage.
Birds that are literally halfasleep--with one brain hemisphere alert and the other sleeping--control which side of the brain remains awake, according to a new study of sleeping ducks. Earlier studies have documented halfbrain sleep in a wide range of birds. The brain hemispheres take turns sinking into the sleep stage characterized by slow brain waves. The eye controlled by the sleeping hemisphere keeps shut, while the wakeful hemisphere's eye stays open and alert. Birds also can sleep with both hemispheres resting at once.
Decades of studies of bird flocks led researchers to predict extra alertness in the more vulnerable, endoftherow sleepers. Sure enough, the end birdstended to watch carefully on the side away from their companions. Ducks in the inner spots showed no preference for gaze direction.
Also, birds dozing(打盹) at the end of the line resorted to singlehemisphere sleep, rather than total relaxation, more often than inner ducks did. Rotating 16 birds through the positions in a four duck row, the researchers found outer birds halfasleep during some 32 percent of dozing
12 percent for birds in internal spots. "We believe this is the first evidence for an animal behaviorally controlling sleep and wakefulness simultaneously in different regions of the brain，"the researchers say.
The results provide the best evidence for a longstanding supposition that singlehemisphere sleep evolved as creatures scanned for enemies. The preference for opening an eye on the lookout side could be widespread, he predicts. He's seen it in a pair of birds dozing sidebyside in the zoo and in a single pet bird sleeping by a mirror. The mirrorside eye closed as if the reflection were acompanion and the other eye stayed open.
Useful as halfsleeping might be, it's only been
such water mammals(哺乳动物) as dolphins, whales, and seals. Perhaps keeping one side of the brain awake allows a sleeping animal to surface occasionally to avoid drowning. Studies of birds may offer unique insights into sleep. Jerome M. Siegel of the UCLA says he wonders if birds' halfbrain sleep "is just the tip of the iceberg(冰山)" He speculates that more examples may turn up when we take a closer look at other species.
11. A new study on birds' sleep has revealed that ________ .
A) halfbrain sleep is found in a wide variety of birds
B) halfbrain sleep is characterized by slow brain waves
C) birds can control their halfbrain sleep consciously
D) birds seldom sleep with the whole of their brain at rest
12. According to the passage, birds often half sleep because ________ .
A) they have to watch out for possible attacks
B) their brain hemispheres take turns to rest
C) the two halves of their brain are differently structured
D) they have to constantly keep an eye on their companions
13. The example of a bird sleeping in front of a mirror indicates that ________.
A) the phenomenon of birds dozing in pairs is widespread
B) birds prefer to sleep in pairs for the sake of security
C) even an imagined companion gives the bird a sense of security
D) a single pet bird enjoys seeing its own reflection in the mirror
14. While sleeping, some water mammals tend to keep half awake in order to ________ .
A) alert themselves to the approaching enemy
B) emerge from water now and then to breathe
C) be sensitive to the everchanging environment
D) avoid being swept away by rapid currents
15. By "just the tip of the iceberg"( Line 2, Para. 8), Siegel suggests that________ .
A) halfbrain sleep has something to do with icy weather
B) the mystery of halfbrain sleep is close to being solved
C) most birds living in cold regions tend to be half sleepers
D) halfbrain sleep is a phenomenon that could exist among other species
11. 正确答案为C)。根据文章第1、3-6段可知，对鸟类睡眠的最新研究表明，它们能够有意识地控制自己的半脑睡眠。这几段举例说明了对这个问题实验的情况。选项A)、B)、D)虽在文章第2 段中也提到了，但那是文献记载的以前研究的情况(Earlier studies have documented...)故均不是正确答案。
12. 正确答案为A)。根据文章第6段The results provide the best evidence for along standing supposition that singlehemisphere sleep evolved as
creatures scanned for enemies.(这些研究结果为一个长久以来的假设提供了最好的证据，即单侧脑睡眠是在生物警惕敌人过程中进化形成的。)
13. 正确答案为C)。根据文章第6段内容：鸟类单侧脑睡眠是在警惕敌人过程中进化而来，此结论还可推而广之。在需要警惕的一侧，鸟儿喜欢睁着一只眼睛……，一对动物园里的鸟儿挨着打瞌睡时 是如此，宠物鸟靠镜子一侧的眼睛闭着，好象镜子中的影子是一个伙伴，而另一只眼睛却睁着， 也说明这种情况。所以选项C)是答案。
14. 正确答案为B)。根据文章第7段第2句Perhaps keeping one side of the brain awake allows a sleeping animal to surface occasionally to avoid
drowning.(也许，保持一侧脑醒着可以使睡眠中的动物不时浮出水面而刁；淹死。)所以B)emerge from water now and then to breathe(不时浮出水面来呼吸)是正确答案。
15. 正确答案为D)。根据文章最后的一段，也就是含有这个短语的上下文。Studies of birds may offer unique insights into sleep...He (Siegel)speculates that more examples may turn up when we take closer look at other species.(对鸟类的研究可能提供对睡眠的独特认识。……他推测当我们对其他物种仔细观察时，就会发现更多的例证。)因此选项D)所说"半侧脑睡眠这种现象可能存在于其他物种"正是"just the tip of iceberg"所表达的意思。
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