Which reaction is catalyzed by carbonic anhydrase? a. HPO42−​+H+⇆H2​PO4−​ b. CO2​ + H2​O⇆H2​CO3​ c. H2​PO4−​+OH−⇆HPO42−​+H2​O d. H2​CO3​⇆HCO3−​+H+