If the graph of an object's position over time is a horizontal line and \( y \) is not equal to 0, then the object is not changing its position. This means the object is at a constant position throughout the time interval.
From this, we can conclude:
The velocity is zero.
This is because the velocity of an object is defined as the change in position over change in time. Since the position is constant (the horizontal line indicates no change in position), the velocity must be zero.
So, the correct response is: The velocity is zero.