5. In vertebrates, the binding of acetylcholine to the ligand-gated ion channels of a skeletal muscle, which are peimeable to both Na+ and K+ ions, will cause _____ at the motor endplate of the muscle cell. (Select the best answer from the choices given, and explain your answer.) (A) repolarization only (B) no change in membrane potential (C) depolarization only (D) hyperpolarization only