What We Know and Don’t Know about Sleep
         Why do we sleep? Up until today, researchers are still trying to find out. Sleep is regarded as oneof the greatest unsolved mysteries of science, even though all animals do it in one form or another.Theories range from brain maintenance to reversing damage from stress suffered while awake, topromoting longevity. However, "none of these theories are well-established, and many aremutually exclusive," according to University of California, Los Angeles (UCLA).Hibernation, a phase during which animals spend the winter in a deep sleep, is one example ofan activity that regulates behavior for survival. A small animal can’t migrate to a warmer climate inwinter, Siegel says. "So it hibernates, effectively cutting its energy consumption and thus its need forfood, remaining secure from predators by burrowing underground." Sleep duration, then, isdetermined in each species by its behavioral patterns such as time requirements of eating, migrationneeds, care of young, and other factors. "However, unlike hibernation...," says Siegel, "sleep is rapidlyreversible – that is, animals can wake up quickly, a unique mammalian adaptation that allows for arelatively quick response to sensory signals."
       Humans fit into this analysis as well. The human brain, albeit just two percent of total bodyweight, consumes 20 percent of total energy used when a person is resting – an amazing ratio. So theenergy savings achieved during sleep have considerable significance. Sleep also has survival benefitsfor humans which include, according to Siegel, “a reduced risk of injury, reduced resourceconsumption and, from an evolutionary standpoint, reduced risk of detection by predators.”        Some people try to ignore the body’s sleep demands. In her fast-paced job as a reporter for asouthern California newspaper, Gwendolyn Driscoll says she "blasts through the day." Arrivinghome late in the evening, she has little time for housework or catching up on her reading, and evenless for sleep. Most nights, she gets about six and half hours. "I could definitely do with another hour,"says 35-year-old Driscoll. "But sleep just isn’t a priority."       Perhaps it should be. Sleep experts say the average adult requires seven to eight hours of sleepper night. Anything less may harm his or her health. Sleep deprivation could affect mental alertnessand increase the risk for diseases. "Sleep is just as important to our overall health as are exercise anda healthy diet," says Carl Hunt, the director of the National Center on Sleep Disorders Research inBethesda, Maryland. Sleep is a biological need, much like food and water. If totally deprived of sleep,humans ultimately die. Yet millions of Americans are increasingly getting too little sleep. Today,Americans on average sleep one hour less per night than they did 20 to 30 years go.        Sleep deprivation has a very negative impact on mental function, creativity, alertness, and theability to participate effectively in everyday interactions. It has been shown to negatively affectlanguage skills, decision-making, and memory. "Without sufficient amounts of sleep, we feel drowsyand are unable to concentrate," Hunt says. He noted that with enough sleep deprivation, some peoplecan develop mood changes and can even begin to hallucinate, all of which can lead to reduced qualityof life.        Not surprisingly, there is also a strong link between sleep deprivation and traffic accidents. Whatmost people don’t realize, researchers say, is that sleep deprivation also accumulates over time. Peoplewho don’t get enough sleep build up a "sleep debt," which can’t be eliminated by getting a little extrasleep on the weekend. "Most people are carrying a fairly large sleep debt and are in fact impaired anddo not seem to know it," Dement and colleagues have published a study that documented the resultsof lowering the sleep debt. "Some of the improvements in performance, in mood, in mental ability,and in energy were really dramatic, almost superhuman," they say.
【題組】46. What is the best paraphrase for the underlined sentence in Paragraph 1?
(A) All of these theories resulted from careful research, but they aren’t yet proven.
(B) Some of these theories make sense, and they should be considered.
(C) These theories are not proven, and they contradict each other.
(D) These theories are similar to each other and are believed by many people.
(E) All of these theories resulted from careful research are proven effective.