If no external forces act on a moving object it will

Stay moving the same speed Hope this helps! ;D

So we want to know what happens to a moving object if no external forces act on it. So Newtons first law states that the object will continue moving with constant velocity or continue to stand still if no external force is acting on the object. So the correct answer is If no external forces act on a moving object it will continue to move with constant velocity. 

Ithink it’s: light bounce if off a mirror