During the Relative Refractory Period,an Initial Threshold-Level Depolarization Is Usually

Multiple Choice

During the relative refractory period,an initial threshold-level depolarization is usually not sufficient to trigger an action potential.Why?

A) Only some Na⁺ channels have returned to their resting position.
B) Only K⁺ channels are still open, so Na⁺ entry is offset by K⁺ loss.
C) Only a few K⁺ channels have returned to their resting position.
D) The statement is incorrect; a threshold-level depolarization always triggers an action potential.
E) Some Na⁺ channels have returned to their resting position and K⁺ channels are still open, so Na⁺ entry is offset by K⁺ loss.