[填空题]Judging from word formation, "shortfall" in "The U.S. saving shortfall is equally stressful" (Line 1, Para.7) probably means ______.

[单项选择]Judging from the context, the word "they" (line 2, Para.4) refer to ______.


A. the security risks
B. the terrorist attacks
C. environmental hazards of over-centralization
D. the security risks, economic expenses, and environmental hazards

[单项选择]Judging from recent surveys, most experts in sleep behavior agree that there is virtually an epidemic of sleepiness in the nation. "I can"t think of a single study that hasn"t found Americans getting【C1】______sleep than they ought to." says Dr. David. 【C2】______people who think they are sleeping enough would probably be【C3】______with more rest. The beginning of our sleep deficit crisis can be【C4】______to the invention of the light bulb a century ago. From diary entries and other personal【C5】______from the 18th and 19th centuries, sleep scientists have reached the【C6】______that the average person used to sleep about 9.5 hours a night. "The best sleep habits once were【C7】______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【C8】______, 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【C9】______they"re doing it," says Dr. David. "They think they"re okay because they can【C10】______on 6.5 hours, when they really need 7.5, 8 or even more to feel ideally【C11】______." Perhaps the most merciless robber of sleep, researchers say, is the【C12】______of the day. Whenever pressures from work, family, friends and community【C13】______, many people consider sleep the least【C14】______item on the agenda. "In our society, you"re considered【C15】______if you say you only need 5.5 hours" sleep. If you say you"ve got to get 8.5 hours, people think you lack【C16】______and ambition." To assess the【C17】______of sleep deficit, researchers have put subjects【C18】______a set of psychological and performance tests requiring them, for instance, to add columns of numbers or recall a passage read to them only minutes earlier. "We"ve found that if you"re sleep-deprived, performance【C19】______," says Dr. David. "Short-term memory is impaired,【C20】______are abilities to make decisions and to concentrate."【C1】
A. less
B. more
C. little
D. much