Four samples are each titrated with the same $\mathrm{HCl}$. The burette readings are noted at the phenolphthalein end point ($R_1$) and at the methyl orange end point ($R_2$), both measured from the initial zero. Each sample contains only $\mathrm{NaOH}$, $\mathrm{Na}{}_2\mathrm{CO}{}_3$, $\mathrm{NaHCO}{}_3$ or a compatible mixture. Select the samples that contain $\mathrm{Na}{}_2\mathrm{CO}{}_3$ together with exactly one other solute.

1. A$R_1=10.0$ mL, $R_2=20.0$ mL
2. B$R_1=15.0$ mL, $R_2=20.0$ mL
3. C$R_1=5.0$ mL, $R_2=20.0$ mL
4. D$R_1=12.0$ mL, $R_2=12.0$ mL