Stroboscopic photography is a commonly used experimental method to study the motion of objects. Photography is done in a dark room, and the flash flashes every once in a while.

A and B, although the two balls of A and B started from the same position and appeared in the same position at the back, this only shows that they have passed the same distance, but A shot five times and B shot three times, so the time is different, and A moves longer than B; Therefore, options A and B are wrong;

C. As shown in Figure A, the ball A travels the same distance at the same time, and the ball A moves in a straight line at a uniform speed. Therefore, option C is correct;

D, Figure B, the distance traveled by ball B is different in the same time, and the distance traveled is longer and longer in the same time, that is, the speed is getting bigger and bigger; Therefore, the d option is wrong.

So choose C.