Which Is Most Directly Responsible for the Falling (Repolarizing) Phase

Multiple Choice

Which is most directly responsible for the falling (repolarizing) phase of the action potential?

A) Voltage-gated Na⁺ channels are opened.
B) The Na⁺, K⁺ pump restores the ions to their original locations inside and outside of the cell.
C) The permeability to Na⁺ increases greatly.
D) ATPase destroys the energy supply that was maintaining the action potential at its peak.
E) The permeability to K⁺ increases greatly while that to Na⁺ decreases.