5. The diagram to the right shows the lowest four energy levels for an electron in hypothetical atom. The electron is excited to the -1 eV level of the atom and transitions to the lowest energy state by emitting only two photons. Which of following energies could not belong to either of the photons?
(A) 2 eV
(B) 4 eV
(C) 5 eV
(D) 6 eV
