A molecule may be represented by three structures having energies E1,E2 and E3, respectively. The energies of these structures follow the order E3<E2<E1, respectively. If the experimental bond energy of the molecule is E0, the resonance energy is :
a. (E1+E2+E3)−E0
b. E0−E3
c. E0−E1
d. E0−E2