Electrons are made to flow in a wire when there is
a) an imbalance of charges in the wire.
b) more potential energy at one end of the wire than the other.
c) a potential difference across its ends.

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.

gas and liquid

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide