Whether an equilibrium is stable or not has got nothing to do with kinetic energy. It has got nothing to do with motion. Yes, if there was enough kinetic energy in a low valley, then an object would be able to roll out of it again.
But everything can escape anything with the right kinetic energy - we call something stable, not because it can't escape at any value of kinetic energy, but because it can't escape at some.
Place a marple on a hill top and another in a valley crest. Which of these positions is stable? The marples can lie still at both, so they are at equilibrium at both positions. But which would we call a "stable" equilibrium? The valley, of course. Because at the slightest offsetting from the exact top-point it will roll away - so we call it unstable - while at the slightest offsetting from the exact bottom-point it will roll back - so we call it stable.
In general, objects want to move the way that decreases the potential energy (that's why objects fall down, if they have the chance, and not up).
At a hill top, the potential energy is lower at all other nearby positions, so the object will roll down.
While at a valley bottom, the potential energy is higher at all nearby positions, so it will not want to go there but will rather stay down at that bottom.
Therefore, option c) is false. Point b is definitely a point of equilibrium, just an unstable equilibrium. If the text book says that c) is a right answer, then that must be a mistake.