Acceleration is defined as the rate at which an object's velocity changes. Velocity is a vector quantity, including both speed and direction. Zero acceleration ($a = 0$) occurs only when the velocity ($v$) remains constant.
Constant velocity implies that neither the speed nor the direction of motion changes.
We examine each option to see if the velocity is constant:
The only situation exhibiting constant velocity, and hence zero acceleration, is the car moving with constant speed on a straight road.
Acceleration is equal to the rate of change of _________.
At uniform speed the acceleration is
At uniform speed the acceleration is