17. For Born Oppenheimer approximation, which of the following statement is correct? (A). The motion of nuclei and the motion of the electrons are coupled. (B). The motion of electrons is much faster than that of nuclei due to their big differences in mass. (C). In the Hamiltonian operator, the electron-nucleus interactions are removed. (D). The electrons and nuclei are considered to have a similar speed. (E). The energy of electrons depends on positions and velocities of nuclei.