单项选择题

What is the main topic of the passage

A．Research on the consequences of sleep-deficit.
B．The epidemic of sleepiness in the modem times.
C．The history of people's sleeping patterns.
D．The minimum of our sleeping hours.

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单项选择题

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 to do so because of their life style and the lack of electricity
D．they were not so dynamic and ambitious as modem people are

单项选择题

The major cause of sleep-deficit of modem people is ______.

A．the endless TV programme in the evenings
B．heavy work load of the day
C．sufficient energy modem people usually have
D．loud noises in the modem cities