A body can have zero velocity and still be accelerated.
A body can have a constant velocity and still have a varying speed.
A body can have a constant speed and still have a varying velocity.
The direction of the velocity of a body can change when its acceleration is constant.
Solution
Speed is a scalar quantity that only number and velocity is a vector which means having magnitude and direction both. In order to have constant velocity the speed needs to be constant. Whereas a body can have constant speed with changing direction (velocity).
When car going roundabout is the perfect example of this situation.