Concept:Stable equilibrium is the state in which a body, when slightly displaced, returns to its original position.
Explanation:In the undulating surface, balls resting at the bottom of valleys are in stable equilibrium.
When such a ball is pushed slightly, it rolls back toward the lowest point.
Balls at the top of hills are in unstable equilibrium.
From the diagram, the lowest valley positions are III, VI and IX.
These positions satisfy the condition for stable equilibrium.
They correspond directly to option C.
Answer:III, VI and IX (Option C).
