阅读理解。 Judging from recent surveys,most experts in sleep behaviour agree that there is virtually an epidemic (流行病) 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 sleepdeficit crisis can be traced back to the invention of the light bulb a century ago.From diary entries and our 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,the 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 in 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 energetic.' Perhaps the most merciless robber of sleep,researchers say,is the complexity of the day. Whenever pressures from work,family,friends and community increase,many people consider sleep the least expensive item on their programme.'In our society,you're considered dynamic if you say you need only 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 sleepdeficit,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 sleepdeficit,performance suffers,' says Dr David.'Shortterm memory is weakened,as are abilities to make decisions and to concentrate.' 1．What is the main topic of the passage?_____ A．Research on the causes and consequences of sleepdeficit. B．The epidemic of sleepiness in the modern times. C．The history of people's sleeping patterns. D．The minimum of our sleeping hours. 2．Which of the following is Dr David's opinion?_____ A．People who think they are sleeping enough are better off than those who don't. B．Some people can remain energetic with only 6.5 hours' sleep a night. C．If they get 8.5 hours' sleep,people will be full of drive and ambition. D．People's mental power suffers if they are lacking in sleep. 3．People in the 18th and 19th centuries slept about 9.5 hours a night because ________. A．they were forced by their parents to do so B．they knew what was best for their health C．they had no electricity D．they were not so dynamic and ambitious as modern people are 4．The major cause of sleepdeficit of modern people is ________. A．the endless TV programmes in the evenings and the Internet B．the pressures of the day C．the sufficient energy modern people usually have D．loud noises in modern cities 5．What does the word 'subjects' in Paragraph 4 mean?______. A．Persons or things being discussed or described. B．Branches of knowledge studied in a school. C．Persons or things being treated in a certain way or being experimented on. D．Any member of a state apart from the supreme ruler.