A．On short trips.
B．On long trips.
C．When flying over cities.
D．When flying at high altitudes,
参考答案A
解析:
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A．It uses nuclear energy.
B．It rests on a cushion of pressurized air.
C．It flies over magnetically activated tracks.
D．It uses a device similar to a jet engine.
A．It is more comfortable than a conventional train.
B．It doesn't require very much track maintenance.
C．It doesn't remain in any station very long.
D．It carries more passengers than a conventional train.
A．Social work.
B．Medical care.
C．Applied physics.
D．Special education.