The correct answer is: D. None of these.
A body is said to be in equilibrium if the net force acting on it is zero. This means that the body is not accelerating in any direction. It can be moving horizontally, vertically, or rotating about its center of gravity, but as long as the net force is zero, it will be in equilibrium.
Option A is incorrect because a body can move horizontally and still be in equilibrium. For example, a car driving at a constant speed is in equilibrium because the net force acting on it is zero.
Option B is incorrect because a body can move vertically and still be in equilibrium. For example, a ball thrown straight up into the air is in equilibrium during its upward motion because the net force acting on it is zero.
Option C is incorrect because a body can rotate about its center of gravity and still be in equilibrium. For example, a spinning top is in equilibrium because the net force acting on it is zero.