The best title for this passage is ______.

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

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