A、NaH<sub>2sub>PO<sub>4sub>--Na<sub>2sub>HPO<sub>4sub>(pK<sub>α1sub>θ=2.12,pK<sub>α2sub>θ=7.20) B、HCOOH--HCOONa(pK<sub>αsub>θ=3.74) C、HAC--NaAC(pK<sub>αsub>θ=4.74) D、NaHCO<sub>3sub>--Na<sub>2sub>CO<sub>3sub>(pK<sub>α1sub>θ=6.38,pK<sub>α2sub>θ=10.25)