单项选择题

How has the use of helicopters developed

A．They are taking the place of high-flying jets.
B．They are used for rescue work only.
C．They have been widely used for various purposes.
D．They are now used for commercial purposes.
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单项选择题
Helicopters are set to motion by means of______.
A．one rotating fan in the centre of the aircraft and others at each end
B．a rotating fan underneath for lifting
C．a rotating device on top
D．a combination of rotating devices in front and on top
单项选择题
According to the passage, people expect that______.
A．helicopters could eventually replace the airliners of today
B．their imaginations fired by the Russian engineer's invention would be realized in the future
C．their fantastic expectations about helicopters could be fulfilled by airliners of today
D．helicopters would someday be able to carry millions of people from place to place as airliners are now doing
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