To answer part (a), if the velocity of an object is zero, it does not necessarily mean that the acceleration is zero. For instance, consider an object that is momentarily at rest at the peak of its trajectory when thrown upward. While its velocity is zero at that exact point in time, it is still experiencing acceleration due to gravity pulling it back down. Therefore, a zero velocity can exist alongside a non-zero acceleration.
Now, for part (b), if the acceleration is zero, this indicates that there is no net force acting on the object, which means the object will continue to move at a constant velocity, or remain at rest. However, this does not imply that the velocity itself must be zero. An object could be moving with a constant velocity (which could be any value, including non-zero) while its acceleration remains zero. In summary, zero acceleration means a constant velocity, which may or may not be zero.