Which of the following characteristics determines when the refractory period ends?

The correct answer for the question that is being presented above is this one: "D. how long it takes for the voltage-gated Na + channels to reactivate at the end of an action potential."

Here are the following choices:

A. how low the membrane potential drops below resting potential during the undershoot phase

B. how long it takes for the voltage-gated Na + channels to close at the end of an action potential

C. how long it takes for the voltage-gated K + channels to close during the undershoot phase

D. how long it takes for the voltage-gated Na + channels to reactivate at the end of an action potential

E. how long it takes for the membrane potential to return to resting potential after the undershoot phase