Which of the following statements correctly describe(s) the driving forces for diffusion of na+ and k+ ions through their respective channels? select all that apply. a. the diffusion of na+ ions into the cell is facilitated by the na+ concentration gradient across the plasma membrane. b. the diffusion of na+ ions into the cell is impeded by the electrical gradient across the plasma membrane. c. the diffusion of k+ ions out of the cell is impeded by the k+ concentration gradient across the plasma membrane. d. the diffusion of k+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. e. the electrochemical gradient is larger for na+ than for k+.