Final answer:
The opening of voltage-gated Na+ channels during an action potential causes depolarization and does not contribute to the repolarization that returns the membrane to its resting potential. Repolarization is achieved by opening voltage-gated K+ channels and inactivating voltage-gated Na+ channels.
Step-by-step explanation:
During an action potential, the action that does not help return the membrane to its resting potential is A.
The opening of voltage-gated Na+ channels. This is because the opening of these channels causes depolarization, not repolarization. The return to resting potential is facilitated by B.
The opening of voltage-gated K+ channels, which allows K+ to leave the cell, and C. The inactivation of voltage-gated Na+ channels, which prevents further influx of Na+ and aids in repolarization.
The movement of Na+ and K+ through their respective channels are crucial in the phases of depolarization and repolarization of an action potential.