Astimulus triggers an action potential by view available hint(s) a stimulus triggers an action potential by causing sodium ions to enter the neuron activating the sodium-potassium pump causing potassium ions to enter the neuron causing sodium ions to leak out of the neuron

The answer would be: causing potassium ions to enter the neuron

Sodium is plenty outside cells while potassium is plenty inside the cell. When the action potential triggered, the sodium will flow into the cells. It won't need help from a pump because the flow is not against the concentration. Potassium will be leaked out in the latter phase.