公共英语考试

【单选题】Birds that are literally half-asleep—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 half-brain 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, end-of-the-row sleepers. Sure enough, the end birds tended to watch carefully on the side away from their companions.Ducks in the inner spots showed no preference for gaze direction.
Also, birds dozing at the end of the line resorted to single-hemisphere 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 half-asleep during some 32% of dozing time versus about 12% 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 long-standing supposition that single-hemisphere 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 side-by-side in the zoo and in a single pet bird sleeping by a mirror. The mirror-side eye closed as if the reflection were a companion and the other eye stayed open.
Useful as half-sleeping might be, it’s only been found in birds and such water mammals 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’ half-brain sleep "is just the tip of the iceberg". He speculates that more examples may turn up when we take a closer look at other species.
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
网考网参考答案：C
网考网解析：
[解析] 第六段后两句，即鸟在镜子前睡觉的例子是对本段前两句的进一步佐证。The preference for opening an eye on the lookout side... 是为了对敌人的进攻保持警觉，而The mirror-side eye closed是因为as if the reflection were a companion(好像镜中的影像是它的同伴一样)。这正是C项的内容。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>