A proton is released from rest in a region of space with a nonzero electric field.

(a) As the proton moves, does the electric potential energy of the system increase, decrease, or stay the same?

(b) Choose the best explanation:

I. As the proton begins to move, its kinetic energy increases. The increase in kinetic energy is equal to the decrease in the electric potential energy of the system.

II. Because the proton has a positive charge, its electric potential energy will always increase.

III. The proton will move perpendicular to the electric field, and hence its electric potential energy will remain the same?