单项选择题

This story is mainly about ______.

A．the distance between the sun and the other stars
B．the problems of traveling to faraway stars
C．what happens when we travel faster than the speed of light
D．the tool we use when we measure the distance of faraway stars

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单项选择题

If a stone moved at the speed of light, it ______.

A．would weigh twice more than it is motionless
B．would weigh as much as it is on earth
C．would weigh less than it is on earth
D．would have no weight at all

单项选择题

Why do we measure the distance in light-years instead of miles

A．Units of light-years sound better.
B．Using light-years reduced the number of figures used.
C．We used to measure distance in light-years long ago.
D．We do not make mistakes when we use light-years.