Answer:
D) The forces acting on it are balanced.
Step-by-step explanation:
Newton's Second Law of motion tells us that for an object to change its uniform state of motion, there must be a NET Force acting on it, thus accelerating it (either increasing its velocity or decreasing it).
Therefore, if we have a situation where an object is moving at constant velocity (uniform motion), that means that there is no NET Force acting on it (it is not either increasing its speed, or decreasing its speed).
Such can happen because: 1) the very specific case where there is actually NO forces acting on it, or 2) because the forces acting on the object are perfectly balanced.
This second situation is a bit more general than the first one we described since zero forces acting on an object is the same as a zero NET force. For example on Earth every object is under the action of the gravitational force like it or not, so an object moving at constant speed on Earth must have other force/s acting on it that perfectly balance.
Thus, the preferred answer from the list would be option: D) The forces acting on it are balanced.