In the diagram, the arrow shows the movement of electric charges through a wire connected to a battery. A battery with an arrow at its top running from left to right. A black line connects the right end of the battery to the left end by making a series of straight lines to form a rectangular box with the battery as part of the bottom side.
What causes the electric charges to flow from one end of the battery to the other?

a balance in electric potential
a balance in resistance
a difference in electric potential
a difference in resistance