How sleep helps US consolidate memories is still largely a mystery. A recent study from the University of Liibeck, in Germany, offers one clue-Subjects were given a list of 46 word pairs to memorize, just before sleep. Then when they reached the deepest stages of sleep, electrical currents were sent through electrodes on their" heads to induce very slow brain waves. Such slow waves were induced at random in the brains of one group of subjects, but not another.
The next morning, the slow-wave group had better recall of the words. Other types of memory were no| improved, and inducing the slow waves later in the night did not have the same eftect. Why and how the slow waves improved memory is not yet understood, but they are thought to alter the strengths of chemical connections, or synapses, between specific pairs of nerve cells in the brain. Memories are "stored" in these synapses: changing the strength of the synapses increases the strength of the memories they store.
It’s not just memory that is improved by sleep. Recent studies indicate that sleep riot only helps store facts, it also helps make connections between them. Ullrich Wagner arid colleagues in Germany used a puzzle in which players were given a string of numbers, and required to make a series of seven calculations based on these numbers. The seventh calculation (which depended on the preceding six) was the" answer. "Participants repeatedly played the same game with the same roles, but different sets of numbers.
The researchers structured the game such that the second calculation always gave the same answer as the seventh calculation-the final answer. If players recognized this rule, they could get to the final answer much faster. Sonic of the players played the game in the morning, then did other things for eight hours or so, then played the game again. Others played the game first in the evening, then slept, then played it again alter awakening. The players who slept were almost three times more likely to have the insight that allowed them to spot the rule.
Why is this important Some sleep researchers believe that for every two hours we spend awake, the brain needs an hour of sleep to figure out what all these experiences mean, and that sleep plays a crucial role in constructing the meaning our lives come to hold. Breakdowns in such sleep-dependent processing may contribute to the development of depression, and may explain why some people who experience horrific traumas go on to develop post-traumatic stress disorder.
What is the main idea of the last paragraph

A:Why sleep is important. B:How sleep can help us. C:What problems lack of sleep may bring. D:How people develop post-traumatic stress disorder.

Judging from recent surveys, most experts in sleep behavior agree that is virtually an epidemic of sleepiness in the nation. "I can’t think of a single study that hasn’t found Americans getting less sleep than they ought to. " says Dr. David. Even people who think they are sleeping enough would probably be better off with more rest.
The beginning of our sleep-deficit crisis can be traced to the invention of the light bulb a century ago. From diary entries and other personal accounts from the 18th 19th centuries, sleep scientists have reached the conclusion that the average person used to sleep about 9.5 hours a night. "The best sleep habits once were forced on us, when we had nothing to do in the evening down on the farm, and it was dark. " By the 1950s and 1960s, that sleep schedule had been reduced dramatically, to between 7.5 and 8 hours, and most people had to wake to an alarm clock. "People cheat on their sleep, and they don’t even realize they’re doing it," says Dr. David. "They think they’re okay because they can get by on 6.5 hours, when they really need 7.5,8 or even more to feel ideally vigorous. "
"Perhaps the most merciless robber of sleep," researchers say, "is the complexity of the day. " Whenever pressures from work, family, friends and community mount, many people consider sleep the least expensive item on his program. "In our society, you’re considered dynamic if you say you only need 5.5 hours’ sleep. If you’ve got to get 8.5 hours, people think you lack drive and ambition. "
To determine the consequences of sleep deficit, researchers have put subjects through a set of psychological and performance tests requiring them, for instance, to add columns of numbers or re call a page read to them only minutes earlier. "We’ve found that if you’re in sleep deficit, perform ance suffers," says Dr. David. "Shot-term memory is weakened, as are abilities to make decision and to concentrate.

Many Americans believe that （　）.

A:sleep is the first thing that can be sacrificed when one is busy B:they need more sleep to cope with the complexities of everyday life C:to sleep is something one can do at any time of the day D:enough sleep promotes people’s drive and ambition

As cold season approaches, many Americans stock up on their vitamin C and Echinacea (紫锥花精油). But fallowing the age -old advice about catching up on sleep might be more important.
Studies have demonstrated that poor sleep and susceptibility (易受影响) to colds go hand in hand, and scientists think it could be a reflection of the role sleep plays in maintaining the body’s defenses.
In a recent study for the Archives of Internal Medicine, scientists followed 153 men and women for two weeks, keeping mack of their quality and duration of sleep. Then, during a five - day period, they quarantined (进行检疫隔离) the subjects and exposed them to cold viruses. Those who slept an average of fewer than seven hours a night, it turned out, were three times as likely to get sick as those who averaged at least eight hours.
Sleep and immunity, it seems, are tightly linked. Studies have found that mammals that require the most sleep also produce greater levels of disease - fighting white blood cells--but not red blood cells, even though both are produced in bone marrow (骨髓) and stem from the same precursor (前体物). And researchers at the Max Planck Institute for Evolutionary Anthropology have shown that species that sleep more have greater resistance against pathogens (病原体).
"Species that have evolved longer sleep durations," the Planck scientists wrote, "appear to be able to increase investment in their immune systems and be better protected. /
What do many Americans do in the effort to avoid cold in winter

A:They take vitamin C and use Echinacea. B:They sleep more as the scientists suggest. C:They try to stay indoors as much as possible D:They sleep less to make time for exercise.

As cold season approaches, many Americans stock up on their vitamin C and Echinacea (紫锥花精油). But fallowing the age -old advice about catching up on sleep might be more important.
Studies have demonstrated that poor sleep and susceptibility (易受影响) to colds go hand in hand, and scientists think it could be a reflection of the role sleep plays in maintaining the body’s defenses.
In a recent study for the Archives of Internal Medicine, scientists followed 153 men and women for two weeks, keeping mack of their quality and duration of sleep. Then, during a five - day period, they quarantined (进行检疫隔离) the subjects and exposed them to cold viruses. Those who slept an average of fewer than seven hours a night, it turned out, were three times as likely to get sick as those who averaged at least eight hours.
Sleep and immunity, it seems, are tightly linked. Studies have found that mammals that require the most sleep also produce greater levels of disease - fighting white blood cells--but not red blood cells, even though both are produced in bone marrow (骨髓) and stem from the same precursor (前体物). And researchers at the Max Planck Institute for Evolutionary Anthropology have shown that species that sleep more have greater resistance against pathogens (病原体).
"Species that have evolved longer sleep durations," the Planck scientists wrote, "appear to be able to increase investment in their immune systems and be better protected. /
What can we learn from the passage

A:Scientists have proved the link between sleep and immunity. B:Mammals that require the most sleep produce more blood cells. C:Species that sleep more have greater resistance against pathogens. D:Red blood cells help the body to fight against diseases.

British teenagers are damaging their health by not getting enough sleep because they are distracted by electronic gadgets in their bedrooms, according to a survey on Tuesday.
The Sleep Council said "junk sleep" could compare with junk food as a major lifestyle matter for teenagers’ parents.
The poll of 1,000 teenagers aged 12 to 16 found that 30 percent managed just 4 to 7 hours’ sleep, even though they are advised to sleep 8 or 9 hours.
Almost a quarter said they fell asleep more than once a week while watching TV, listening to music or using other electronic gadgets.
"This is a really worrying trend," said Dr Chris Idzikowski of the Edinburgh Sleep Centre.
"What we are seeing is the result coming out of ’junk sleep’ . It has neither length nor quality, both of which are important to feed the brain with the rest it needs to perform properly at school. "
Nearly all the teenagers had a phone, music system or a TV in their bedrooms, and about two-thirds of the teenagers had all three of these things.
Almost one in five teenage boys said the quality of their sleep had been influenced by their TVs or computers being left on. The survey also found that 40 percent of teenagers felt tired each day, with girls aged 15 to 16 feeling the worst.
However, only 11 percent said they were bothered by the lack or bad quality of sleep.
"I’m staggered that so few teenagers make the link between getting enough good quality sleep and bow they feel during the day," Idzikowski said. "Teenagers need to realize the fact that to feel well, perform well and look good, they need to do something about their sleep. /
The best title for the passage is ______.

A:How Much Sleep Should Teenagers Get B:Teenagers Should Get More Sleep C:"Junk Sleep" Damaging Teenagers’ Health D:New Study of Teenagers’ Sleep

British teenagers are damaging their health by not getting enough sleep because they are distracted by electronic gadgets in their bedrooms, according to a survey on Tuesday.
The Sleep Council said "junk sleep" could compare with junk food as a major lifestyle matter for teenagers’ parents.
The poll of 1,000 teenagers aged 12 to 16 found that 30 percent managed just 4 to 7 hours’ sleep, even though they are advised to sleep 8 or 9 hours.
Almost a quarter said they fell asleep more than once a week while watching TV, listening to music or using other electronic gadgets.
"This is a really worrying trend," said Dr Chris Idzikowski of the Edinburgh Sleep Centre.
"What we are seeing is the result coming out of ’junk sleep’ . It has neither length nor quality, both of which are important to feed the brain with the rest it needs to perform properly at school. "
Nearly all the teenagers had a phone, music system or a TV in their bedrooms, and about two-thirds of the teenagers had all three of these things.
Almost one in five teenage boys said the quality of their sleep had been influenced by their TVs or computers being left on. The survey also found that 40 percent of teenagers felt tired each day, with girls aged 15 to 16 feeling the worst.
However, only 11 percent said they were bothered by the lack or bad quality of sleep.
"I’m staggered that so few teenagers make the link between getting enough good quality sleep and bow they feel during the day," Idzikowski said. "Teenagers need to realize the fact that to feel well, perform well and look good, they need to do something about their sleep. /
The purpose of this passage is to ______.

A:encourage teenagers to sleep as much as possible B:discourage teenagers’ from staying up late at night C:inform people of the damage "junk sleep" does to teenagers’ health D:instruct people how to have a long and good-quality sleep

British teenagers are damaging their health by not getting enough sleep because they are distracted by electronic gadgets in their bedrooms, according to a survey on Tuesday.
The Sleep Council said "junk sleep" could compare with junk food as a major lifestyle matter for teenagers’ parents.
The poll of 1,000 teenagers aged 12 to 16 found that 30 percent managed just 4 to 7 hours’ sleep, even though they are advised to sleep 8 or 9 hours.
Almost a quarter said they fell asleep more than once a week while watching TV, listening to music or using other electronic gadgets.
"This is a really worrying trend," said Dr Chris Idzikowski of the Edinburgh Sleep Centre.
"What we are seeing is the result coming out of ’junk sleep’ . It has neither length nor quality, both of which are important to feed the brain with the rest it needs to perform properly at school. "
Nearly all the teenagers had a phone, music system or a TV in their bedrooms, and about two-thirds of the teenagers had all three of these things.
Almost one in five teenage boys said the quality of their sleep had been influenced by their TVs or computers being left on. The survey also found that 40 percent of teenagers felt tired each day, with girls aged 15 to 16 feeling the worst.
However, only 11 percent said they were bothered by the lack or bad quality of sleep.
"I’m staggered that so few teenagers make the link between getting enough good quality sleep and bow they feel during the day," Idzikowski said. "Teenagers need to realize the fact that to feel well, perform well and look good, they need to do something about their sleep. /
According to the passage, which of the following statements is NOT true

A:"junk food" and "junk sleep" are equally bad lifestyles. B:Teenagers are advised to sleep 8 or 9 hours. C:TVs or computers left on may affect the sleep quality of teenagers. D:Most teenagers take enough good quality sleep seriously.

{{B}}第二篇{{/B}}

Though not stated, the author implied that______.

A:American drug abuse is connected with toss of sleep B:American students’ poor results result from lack of sleep C:Americans could be more effective with enough sleep D:Accidents in the states could be reduced by more sleep

{{B}}第三篇{{/B}}

Many Americans believe that ______.

A:sleep is the first thing that can be sacrificed when one is busy B:they need more sleep to cope with the complexities of everyday life C:to sleep is something one can do at any time of the day D:enough sleep promotes people’s drive and ambition

As cold season approaches, many Americans stock up on their vitamin C and Echinacea(紫锥 花精油). But following the age -old advice about catching up on sleep might be more important.
Studies have demonstrated that poor sleep and susceptibility (易受影响) to colds go hand in hand, and scientists think it could be a reflection of the role sleep plays in maintaining the body’s defenses.
In a recent study for the Archives of Internal Medicine, scientists followed 153 men and women for two weeks, keeping track of their quality and duration of sleep. Then, during a five - day period, they quarantined(进行检疫隔离) the subjects and exposed them to cold viruses. Those who slept an average of fewer than seven hours a night, it turned out, were three times as likely to get sick as those who averaged at least eight hours.
Sleep and immunity, it seems, are tightly linked. Studies have found that mammals that require the most sleep also produce greater levels of disease -fighting white blood cells—but not red blood cells, even though both are produced in bone marrow(骨髓) and stem from the same precursor(前体物). And researchers at the Max Planck Institute for Evolutionary Anthropology have shown that species that sleep more have greater resistance against pathogens (病原体).
"Species that have evolved longer sleep durations, "the Planck scientists wrote, "appear to be able to increase investment in their immune systems and be better protected. /
What can we learn from the passage

A:Scientists have proved the link between sleep and immunity. B:Mammals that require the most sleep produce more blood cells. C:Species that sleep more have greater resistance against pathogens. D:Red blood cells help the body to fight against diseases.