Energy in Capacitors: an Ideal Parallel-Plate Capacitor Consists of a Set

Energy in capacitors: An ideal parallel-plate capacitor consists of a set of two parallel plates of area A separated by a very small distance d. When the capacitor plates carry charges +Q and -Q, the capacitor stores energy U₀. If the separation between the plates is doubled, how much electrical energy is stored in the capacitor?

A) 4U₀
B) 2U₀
C) U₀
D) U₀/2
E) U₀/4