Ans: C)The pony is accelerating around the track.
Speed is a scalar quantity which expresses how fast an object is moving
Velocity (v) is a vector which expresses both how fast the object is moving and in what direction it is moving
v = distance/time
Acceleration is the rate of change of velocity, hence it is a vector
a = v/t
A body will accelerate if there is a change either in the magnitude or direction of velocity or if both change.
Since the pony is travelling around a track (circle) at constant speed, the magnitude does not change however, the direction keeps changing. Hence, the pony will be accelerating around the track.