What are acids and bases according to Arrhenius theory?

Label the conjugate acid-base pair in the following reactions:

a. $\mathrm{HCl}+{\mathrm{H}}_2\mathrm{O}\rightleftarrows {\mathrm{H}}_3{\mathrm{O}}^{+}+{\mathrm{Cl}}^{-}$.

b. ${\mathrm{CO}}_3^{2-}+{\mathrm{H}}_2\mathrm{O}\rightleftarrows {\mathrm{OH}}^{-}+{\mathrm{HCO}}_3^{-}$.