单项选择题
A．work rapidly B．be large and expensive C．be easy to use D．be used for fun
A．we will notice that it is not moving B．we cannot tell whether or not it still exists C．it will be brighter than the moon D．it is four years that the light we can see will reach us
A．have to travel a greater distance B．move less quickly C．travel much quickly D．be less powerfull