Answer:
C) a potential difference across its ends.
Explanation:
We know , according to Ohm's law, at a constant temperature, current flows through a circuit is directly proportional to the voltage applied.
Here R is resistance provide by circuit.

Also, currents flows in the opposite direction of electrons. If current flows then only electron flows.
From Ohm's law , current flows only when their is a potential difference.
Therefore, same goes with electrons as they flow only when current flows electrons.
C) Option is correct.