Treat the energy costs of eclipsing interactions in butane as additive: H/H = 4.0, $\mathrm{CH}{}_3$/H = 6.0, $\mathrm{CH}{}_3$/$\mathrm{CH}{}_3$ = 11.0 kJ/mol. The fully eclipsed conformation (dihedral $0^{\circ }$) is higher in energy than the partially eclipsed conformation (dihedral $120^{\circ }$) by:

1. A$3.0\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
2. B$11.0\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
3. C$7.0\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
4. D$19.0\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$