Which of the following is true regarding the generation of a membrane potential?
a. Both potassium and sodium ions can "leak" through the cell membrane due to diffusion.
b. In the polarized state, sodium and potassium ion concentrations are in static equilibrium.
c. The maintenance of the potential is based exclusively on diffusion processes.
d. When the sodium-potassium pump is activated, potassium is pumped into the cell twice as fast as the sodium is pumped out, thus causing the membrane potential.