If an object's acceleration is zero, what does this indicate about its motion?

When an object's acceleration is zero, it indicates that the velocity of the object is constant. This means that the object is either at rest (not moving at all, maintaining a velocity of zero) or moving at a constant speed in a straight line (not changing its speed or direction).

In the context of the choices provided, the motion described by the correct answer is that the object is moving at a constant speed. This means that if the object started moving, it would continue moving without increasing or decreasing its speed.

While being at rest can also be a scenario where acceleration is zero, the specific implication of "moving at a constant speed" applies to situations where motion is occurring without any change in speed. Therefore, this answer accurately captures one of the key principles of motion in physics, where constant acceleration (zero acceleration) means the velocity doesn’t change, indicating a steady state of motion that can include both rest and constant speed.