A body is observed to be at rest at a certain instant. Which conclusion is most justified?

The underlying principle is that equilibrium is determined by forces and moments, not by an instantaneous value of velocity. 1. A body can have zero velocity at one instant and still accelerate afterward. 2. For equilibrium, both $\vec F_{\text{net}}=0$ and net moment $=0$ must hold. 3. The example of a ball at the highest point of its upward motion shows this clearly: its velocity is momentarily zero, but gravity still acts, so it is not in equilibrium. Why the distractors are tempting: A is a common misconception that rest implies equilibrium, but momentary rest is not enough. B is false because forces can act even when velocity is zero. D is false because zero velocity at an instant does not guarantee zero acceleration.