单项选择题

Babies sleep much longer than adults each day because ______.

A．they have nothing else to do day and night
B．they need sleep to help develop brains and bodies
C．adults find it difficult to fall asleep at night
D．adults have quite a lot of things to do during the day
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单项选择题
According to the passage, when could people start using a maglev commercially A) In 5 years. C) In 20 years. B) In 10 years. D) In more than 20 years.
A．According to the passage, when could people start using a maglev commercially
B．In 5 years.
C．In 10 years.
D．In 20 years.
E．In more than 20 years.
单项选择题
Argonne believes that people should regard maglev transportation as ______.
A．safe, efficient high-speed trains
B．the most exciting form of transportation for the future
C．a kind of aircraft
D．the most economical form of transportation
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