Answer
See the answer below.
Work Step by Step
a) Acid/Conj. base: $HCO_2H/HCO_2^-$, base/conj. acid: $H_2O/H_3O^+$
b) Acid/Conj. base: $H_2S/HS^-$, base/conj. acid: $NH_3/NH_4^+$
c) Acid/Conj. base: $HSO_4^-/SO_4^{2-}$, base/conj. acid: $OH^-/H_2O$