The correct answer is (C) A balance (between opposing forces). A state of rest between equal and opposing forces or effects; a condition of balance between any opposing influences or powers. Also, the condition when a chemical reaction and its reverse action occur at the same rate.

Equilibrium comes from Latin aequilibrium, (aequi + libra [balance] + ium).

Examples of use:

• As her foot slid out below her on the ice, she lost her equilibrium.
• He lost his equilibrium after taking only a few steps on the narrow iron rail.