单项选择题

How has the use of helicopters developed

A．They have been widely used for various purposes.
B．They are taking the place of high-flying jets.
C．They are used for rescue work.
D．They are now used exclusively for commercial projects.

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单项选择题

Helicopters work with the aid of ______

A．a combination of rotating devices in front and on top.
B．a rotating device topside.
C．one rotating fan in the center of the aircraft and others at each end.
D．a rotating fan underneath for liftin

单项选择题

People expect that ______.

A．the airliners of today would eventually be replaced by helicopters
B．helicopters would someday be able to transport large number of people from place to place as airliners are now doing
C．the imaginations fired by the Russian engineer's invention would become a reality in the future
D．their fantastic expectations about helicopters could be fulfilled by airliners of today

单项选择题

Where is the engineer who realized the ancient-dream from

A．China
B．Italy
C．Canada
D．Russia

单项选择题

How has the use of helicopters developed

A．They have been widely used for various purposes.
B．They are taking the place of high-flying jets.
C．They are used for rescue work.
D．They are now used exclusively for commercial projects.

单项选择题

What is said about the development of the helicopter

A．Helicopters have only been worked on by man since 1940.
B．Chinese children were the first to achieve flight in helicopters.
C．Helicopters were considered more dangerous than the early airplanes.
D．Some people thought they would become widely used by average individuals.

单项选择题

Under what conditions are helicopters found to be absolutely essential

A．For overseas passenger transportation.
B．For extremely high altitude flights.
C．For high-speed transportation.
D．For urgent mission to places inaccessible to other kinds of craft.