单选题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 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 and 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 hours or even more to feel ideally vigorous. " Perhaps the most merciless robber of sleep, researchers say, is the complexity of the day. When ever pressures from work, family, friends and community mount, many people consider sleep the least expensive item on his programme. "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 recall a passage read to them only minutes earlier. "We've found that if you're in sleep deficit, performance suffers," says Dr David. "Short-term memory is weakened, as are abilities to make decisions and to concentrate. /

单选题Whycouldn'tthemanopenthedoor?

单选题{{B}}Part A{{/B}}{{I}} You will hear 10 short dialogues. For each dialogue, there is one question and four possible answers. Choose the correct answer A.,B. ,C. or D. , and mark it in your test booklet. You will have 15 seconds to answer the question and you will hear each dialogue ONLY ONCE. Now look at question 1.{{/I}}

单选题[此试题无题干]

单选题It's spring now. It's getting ______ . A. warmer and warmer B. colder and colder C. wamer and colder

单选题Whatdoyoulearnabouttheman?

单选题 IQuestions 14-17 are based on the following dialogue./I

单选题Whatdoesthewomanmean?

单选题According to the passage" about US $ 116 billion are required to give minimum comfort to these people by the turn of the century--less than US $ 10 billion per year", do you think which year was the article written?

单选题[此试题无题干]

单选题The government of the developed countries may prefer to a ______ population.

单选题What are the two speakers going to do?

单选题What might be the title of the passage?