See attached photos and written questions

During an action potential, the inside of the cell membrane becomes more positive than the outside. Why does this happen?

a.
During depolarization, the sodium ions rush in and the potassium ions have not begun rushing out, making the inside more positive.

b.
During depolarization, the potassium ions rush in and the sodium ions have begun rushing out, making the inside more positive.

c.
During depolarization, the sodium ions rush in and the potassium ions have begun rushing out, making the outside more positive.

d.
During depolarization, the sodium ions rush in and the potassium ions have not begun rushing out, making the outside more positive.