单项选择题

According to Dr. David, Americans ______.

A．are ideally vigorous even under the pressure of life
B．often neglect the consequences of sleep deficit
C．do not know how to relax themselves properly
D．can get by on 6.5 hours of sleep

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单项选择题

It can be concluded from the passage that one should sleep as many hours as is necessary to ______.

A．improve one's memory dramatically
B．be considered dynamic by other people
C．maintain one's daily schedule
D．feel energetic and perform adequately

单项选择题

Many Americans believe that ______.

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