Which of the following correctly describes a compound action potential?

a. It occurs when multiple neurons fire action potentials at the same time within a nerve bundle.

b. It occurs when an action potential passes through gap junctions from a presynaptic neuron to a postsynaptic neuron and continues down the length of the postsynaptic neuron without interruption.

c. It occurs when a single neuron fires action potentials repeatedly over a prolonged period of time.

d. It occurs when a single neuron fires a stronger than normal action potential due to the effects of neuromodulators.