Answer:
Option A. Sodium is needed to generate an action potential.
Step-by-step explanation:
Action potentials are generated by the special types of the voltage-gated channels which are embedded in the plasma membrane of the cell.
These channels are shut when the membrane potential is near zero and the voltage-gated channels open only when the membrane potential is more than the threshold voltage.
When the channels are open then they allow the flow of sodium ions which ultimately changes the electrochemical gradient which rises the membrane potential. This rise in membrane potential generates the action potential.