Answer: Box B
Explanation:
A stable system refers to one on which balanced forces act i.e. the net force on the system is zero and if any unbalanced force acts, the system comes back to its initial stable equilibrium position.
Box A is not a stable system because if any unbalanced force would act on it, its position would change. Box A would topple. It would not come back to its current state. A unstable system has narrow width and high center of mass from the base.
On the other hand, Box B is a stable system. Any unbalanced force would not change its current state. It would come back to its equilibrium state and would not topple over. A stable system has wider base and low center of mass.
