Final answer:
The Na+ and K+ ions must move back to their original compartments, and the Na+ inactivation gate must open and the Na+ activation gate must close before a second action potential can begin.
Step-by-step explanation:
The correct answer is D) the Na+ and K+ ions that moved in/out of the cell must move back to their original compartments; the Na+ inactivation gate must open; and the Na+ activation gate must close.
Before a second action potential can begin, several steps must occur. During the absolute refractory period, another action potential cannot start because the inactivation gate of the voltage-gated Na+ channel is closed and the Na+ activation gate is open. This prevents the flow of Na+ ions into the cell, which depolarizes the cell and initiates an action potential. However, the other options listed in the answer choices are all steps that must occur before a second action potential can begin. The movement of Na+ and K+ ions back to their original compartments helps to restore the resting state of the cell after an action potential, and the opening and closing of the Na+ gates are important for regulating the flow of Na+ ions during depolarization and repolarization.