单项选择题

A．Crowded air traffic.
B．The large size of airplanes.
C．Mistakes by air traffic controllers.
D．Bad weather.
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单项选择题
A．Synthetic fuel.B．Solar energy.C．Alcohol.D．Electricity.
A．Synthetic fuel.
B．Solar energy.
C．Alcohol.
D．Electricity.
单项选择题
The author is convinced that the eyes are________.
A．of extreme importance in expressing feelings and exchanging ideas
B．something through which one can see a person’’s inner world
C．of considerable significance in making conversations interesting
D．something the value of which is largely a matter of long debate
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