Answer:
The velocity is constant at 4km/h.
Explanation:
Velocity - time graph is any graph that describes the relationship between velocity and time.Since, acceleration is the ratio of change of velocity to time, the slope gives us the acceleration.
From the given graph,it is seen at velocity of 4 m/s, the body's time is increasing. However we can see a straight line parallel to x-axis is on that velocity (4km/h).It means that the change of velocity is constant,i.e.,the body is maintaining the same velocity for an increase in time. Hence,the slope is zero or acceleration is zero.
Hence, option C is correct,the velocity is constant.