What Causes the Refractory Period in Sodium Channels After an Action

What causes the refractory period in sodium channels after an action potential has been initiated? (Select all correct responses)

A) The sodium channels must close before they can be reopened in response to another stimulus.
B) The ion channel can only transform from the inactivated to the closed conformation after the inactivating peptide has swung out of the pore opening.
C) The ion channel can only transform from the closed to the inactivated conformation after the inactivating peptide has swung out of the pore opening.
D) The inactivating peptide must bind to the pore opening more tightly before the channel can be restimulated.