Questions: The absolute refractory period: - allows another action potential to occur before a previous one has completed if the frequency is great enough - the period of time between hyperpolarization and repolarization - allows many action potentials to be produced at the same time if the stimulus is strong enough - prevents another action potential from starting until a previous one has been completed

The answer is the fourth one: prevents another action potential from starting until a previous one has been completed.

Explanation for each option:

1. Allows another action potential to occur before a previous one has completed if the frequency is great enough: This is incorrect. The absolute refractory period is a phase during which no new action potential can be initiated, regardless of the strength or frequency of the stimulus.

2. The period of time between hyperpolarization and repolarization: This is incorrect. The absolute refractory period occurs during the depolarization and repolarization phases of the action potential, not between hyperpolarization and repolarization.

3. Allows many action potentials to be produced at the same time if the stimulus is strong enough: This is incorrect. During the absolute refractory period, no action potentials can be produced, no matter how strong the stimulus is.

4. Prevents another action potential from starting until a previous one has been completed: This is correct. The absolute refractory period ensures that each action potential is a separate, all-or-nothing event, preventing the initiation of another action potential until the previous one has finished.

Summary: The absolute refractory period prevents another action potential from starting until a previous one has been completed.