Which mixtures are buffer solutions?

I.     \({\text{KHS}}{{\text{O}}_{\text{4}}}{\text{(aq)}}\) and \({{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{4}}}{\text{(aq)}}\)

II.     \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COONa(aq)}}\) and \({\text{C}}{{\text{H}}_{\text{3}}}{\text{COOH(aq)}}\)

III.     \({\text{HCOOK(aq)}}\) and \({\text{HCOOH(aq)}}\)

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

C