Which statement describes the most important process in the development of a resting membrane potential?

I assume from the option that we are looking at a cell that has or is undergoing and action potential. 1 is not a major component of the resting membrane potential, 2 sodium wants into a cell based on concentration gradients, 3 if potassium leaves the cell becomes less positive, 4 the action is true but this is what leads us to an action potential not resting membrane potential. 5 is the best answer this is what happens after the peak of the action potential curve. The potassium voltage gated channels open and potassium leaves the cell going down its concentration gradient, the cell becomes more negative to counterbalancing the sodium intake and returning closer to resting values. The cell is even out by the action of the ATP dependent sodium/potassium pumps but that is not an option. The answer I give is 5.