Toward the End of the Relative Refractory Period, the Continued

Toward the end of the relative refractory period, the continued decrease in stimulus intensity required to initiate an action potential is caused by

A) the number of sodium channels whose inactivation gate has not opened.
B) increased potassium permeability.
C) decreased sodium permeability.
D) closure of the sodium activation gate.
E) decreased potassium permeability.