2-Bromo-2,3-dimethylbutane, $(\mathrm{CH}{}_3){}_2\mathrm{CBr}-\mathrm{CH}(\mathrm{CH}{}_3){}_2$, is treated separately with $\mathrm{NaOEt}$/ethanol and with $(\mathrm{CH}{}_3){}_3\mathrm{COK}$/$(\mathrm{CH}{}_3){}_3\mathrm{COH}$. Which statements are correct?

1. A$\mathrm{NaOEt}$/ethanol gives mainly 2,3-dimethylbut-2-ene.
2. B$(\mathrm{CH}{}_3){}_3\mathrm{COK}$/$(\mathrm{CH}{}_3){}_3\mathrm{COH}$ gives mainly 2,3-dimethylbut-1-ene.
3. C$(\mathrm{CH}{}_3){}_3\mathrm{COK}$/$(\mathrm{CH}{}_3){}_3\mathrm{COH}$ gives mainly 2,3-dimethylbut-2-ene.
4. DThe substrate has seven beta-hydrogens in total.