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【C4】______
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Birds are literally half-asleep--with one brain hemisphere alert and the other sleeping, 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 (打盹) 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 32 percent of dozing time versus about 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 long-standing supposition that single- hemisphere sleep evolved as creatures scanned for enemies. The preference for opening an eye on the. lockout 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 (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' half-brain 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.
A new study on birds' sleep has revealed that ______
The wandering ship was a dramatic symbol for a problem plaguing our age. In 1987, the ship, loaded with thousands of tons of New York garbage, spent weeks wandering from one port to another in search of a dump before finally returning home, mission unaccomplished.
New York, like other communities throughout the world is running out of space to put its trash. As throwaway societies, the US and other industrialized countries expect their garbage to be picked up by trucks that magically transported the refuse to some out-of-sight incinerator(焚化炉) or dump. But in the developing counties of Asia, Africa and Latin America, thousands of tons of trash collected daily are thrown into open dumps, where it feeds huge populations of rats that swarm through poor neighborhoods.
"The world is literally swimming in garbage," says a scientist, "Communities worldwide are being forced to confront the problem." Green Peace spokesman Bryan Bence adds, "The crisis in garbage stems in part from the fact that we've ignored long-term disposal problem in favor of cheap quick fixes."
The garbage glut (过选剩) has inspired many communities in the U.S., Japan and Western Europe to start recycling programs. Once considered a curious counter culture activity recycling has moved firmly into the mainstream.
Recycling involves separating usable products from trash, processing them so they can be substituted for more expensive raw materials and returning them to the marketplace as parts of new products. Many countries now have mandatory recycling programs, and others plan to follow the trend soon. Most notably, Japan has stood out as a model and leader of the waste management trend, recycling an estimated 65 percent of its waste. "That's what we should do, to the garbage crisis", says David Antonioli, a staff member with the New York Public Interest Research Corp. "The earth is not a dump!"
According to the passage, which of the following statements is TRUE？
Many theories concerning the causes of juvenile delinquency (青少年犯罪) focus either on the individual or on society as the major contributing influence. Theories 【C1】______ on the individual suggest that children engage in criminal behavior. 【C2】______ they were not sufficiently penalized for previous misdeeds or that they have learned criminal behavior. through 【C3】______ with others. Theories focusing on the role of society suggest that children commit crimes in response to their failure to rise above their socioeconomic status 【C4】______ as a rejection of middle-class values.
Most theories of juvenile delinquency have focused on children from disadvantaged families, 【C5】______ the fact that children from wealthy homes also commit crimes. The latter may commit crimes for lack of adequate parental control. All theories, however, are tentative and are 【C6】______ to criticism.
Changes in the social structure may indirectly 【C7】______ juvenile crime rates. Families have also 【C8】______ changes these years. More families consist of one parent households or two working parents; 【C9】______ , children are likely to have less supervision at home, 【C10】______ was common in the traditional family 【C11】______ . This lack of parental supervision is thought to be an influence on juvenile crime rates. Other 【C12】______ causes of offensive acts include frustration or failure in school, the increased 【C13】______ of drugs and alcohol, and the growing 【C14】______ of child abuse and child neglect. All these conditions tend to increase the probability of a child committing a criminal act, 【C15】______ a direct causal relationship (因果关系) has not yet been established.
【C1】______
MOUNTAIN CLIMBING
One of the most difficult but rewarding of pastimes is the sport of mountain climbing. Mountain climbing can be divided into two categories, rock climbing and ice climbing, and the modern climber must【B1】______ many different skills. Rock climbing 【B2】______ a combination of gymnastic ability, imagination and observation, but perhaps the most necessary skill is being able to 【B3】______ out how much weight a padicular rock will 【B4】______ Mountaineers climb in groups of three or four, each climber at a distance of approximately six metres from the next. Usually one person climbs while the other climbers 【B5】______ hold of the rope. The most experienced climber goes first and 【B6】______ the other climbers which 【B7】______ to go. When the leader has reached a good position, he or she makes the rope secure so that it is【B8】______ for the others to follow.
Since much mountain climbing 【B9】______ place in bad weather, snow skills 【B10】______ a very important part. Ice axes are used for 【B11】______ steps into the snow, and for testing the ground. Climbers always tie themselves 【B12】______ so that, if the leader does fall, he or she can be held by the others and 【B13】______ back to safety. The number of dangers 【B14】______ by climbers is almost endless. Yet perhaps the most difficult part of the sport is the physical effort needed when the air has little oxygen. The 【B15】______ of oxygen can leave mountaineers continually out of breath.
【B1】______
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