单项选择题

What serves as the evidence that man is changing

A．Man has got stronger eyes now than he ever had.
B．Man's hair is getting thinner and thinner.
C．Man's arms and legs have become lighter and weaker.
D．Man has been growing taller over the past 500 years.

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单项选择题

What is the passage mainly talking about

A．The reason why the Wright brothers succeeded in manned flight.
B．The role the internal combustion engine played in the Wright brothers' experiments.
C．The Wright brothers' experience as pilots.
D．The importance of gliders to the development of airplane.

单项选择题

Why does the author suggest that the experiments with the wind tunnel were important

A．Because they allowed the Wright brothers to decrease the weight of their airplane.
B．Because they resulted in a three-axis control for their airplane.
C．Because they were important in the refinement of the wings for their airplane.
D．Because they used the data to improve the engine for their airplane.