[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 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
A. the performance tests used in the study of sleep deficit
B. special branches of knowledge that are being studied
C. people whose behavior or reactions are being studied
D. the psychological consequences of sleep deficit

[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 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
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