5. Once acetylcholine binds to its receptor in the postsynaptic membrane, the membrane first becomes to open _______ channel, resulting in a depolarization. Then, followed by an outward flow of ______ , resulting in a hyperpolarization. (A)
(B) K⁺ , Cl⁻ (C)
(D) Na⁺ , K⁺ (E) Na⁺