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 over time. This indicates that the object is at rest.
The true statement about the object's motion is:
The velocity is zero.
The other options are not applicable because:
- The acceleration would be zero because the object is not changing its velocity (it is at rest).
- There cannot be a constant and non-zero velocity or non-zero acceleration if the position is constant.
- There cannot be negative acceleration if there is no movement.
Therefore, the correct response is The velocity is zero.