"Stroboscope photography" is an experimental method commonly used when studying the movement of objects. Photography is done in a darkroom. Fix the camera on the ground and keep the shutter open

A. The intervals between adjacent balls are the same, but the distances are different, so the balls are not moving in a straight line at a uniform speed; therefore A is wrong;

B. The intervals between adjacent balls The time is the same, and the separation distance is also the same; therefore, the ball moves in a straight line at a uniform speed; therefore, B is correct;

C. The separation time of adjacent balls is the same, and the separation distance is increasing, which means that the ball is accelerating. Movement; therefore C is wrong;

D. The intervals between adjacent balls are the same and the distance between them is decreasing, which means the balls are decelerating; therefore D is wrong;

Therefore Choose B.