At the Beginning of the Refractory Period,why Does the Charge

Multiple Choice

At the beginning of the refractory period,why does the charge within a neuron from positive to negative?

A) An inhibitory postsynaptic potential is produced.
B) Sodium channels open allowing sodium to leave the neuron.
C) Potassium channels open allowing potassium to leave the neuron.
D) The concentration of negatively charged proteins increases.