单项选择题

Under which of the following conditions are helicopters found to be absolutely essential

A．For extremely high altitude flights.
B．For urgent mission to places inaccessible to other kinds of craft.
C．For rescue work.
D．For high-speed transportation.
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单项选择题
What is said about the development of the helicopters from the passage
A．People came up with the conceptual idea of a helicopter in this century.
B．Helicopters were thought to be much more dangerous than the early airplanes.
C．Chinese children were the first to experience flights in helicopters.
D．Some people thought that helicopters would develop into popular use one day.
单项选择题
According to the analysis, compared with normal children today, children treated for mental illness 50 years ago______.
A．were less isolated physically
B．were probably less self-centered
C．probably suffered less from anxiety
D．were considered less individualistic
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