The Absolute Refractory Period Occurs Because

Multiple Choice

 The absolute refractory period occurs because

A) the cell is hyperpolarized, requiring a larger than normal stimulus in order to form another action potential.
B) it takes time for the sodium-potassium pumps to return ion concentrations to the normal resting state.
C) only one action potential at a time can travel the length of an axon.
D) sodium channels cannot reopen until the membrane regains its resting potential.