If the graph of an object's position over time is a horizontal line and y is not equal to 0, this indicates that the object's position does not change over time.
When the position is constant, the following must be true:
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The velocity is zero. This is because there is no change in position over time, which means that the object is not moving.
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The acceleration, which is the rate of change of velocity, is also zero in this case since the velocity itself does not change.
Therefore, the correct response is:
The velocity is zero.