Which form of the Henderson-Hasselbalch equation should be used for a solution containing H₃A and H₂A-?

pH = pK_a2 + log([HA^2-]/[H₂A^-])

pH = pK_a3 + log([H₃A]/[A^3-])

pH = pK_a1 + log([H₂A^-]/[H₃A])

pH = pK_a3 + log([A^3-]/[H₂A^-])