12. In the Born-Oppenheimer approximation as used in quantum chemistry, which statement is most accurate?
(A) Nuclear and electronic motions are treated with the same Hamiltonian and solved simultaneously.
(B) Nuclear motion is neglected entirely; only electrons are considered to exist.
(C) The total molecular wavefunction is approximated as a product of an electronic part and a nuclear part because nuclei move much more slowly than electrons.
(D) Electron-nuclear Coulomb interactions are ignored so that electrons move in a field of non-interacting nuclei.
(E) The approximation is only valid for atoms but not for molecules.