Which species behave as Brønsted-Lowry acids in the following reversible reaction?

\[{{\text{H}}_2}{\text{PO}}_4^ - ({\text{aq)}} + {\text{C}}{{\text{N}}^ - }({\text{aq)}} \rightleftharpoons {\text{HCN(aq)}} + {\text{HPO}}_4^{2 - }({\text{aq)}}\]

A.     HCN and \({\text{C}}{{\text{N}}^ - }\)

B.     HCN and \({\text{HPO}}_4^{2 - }\)

C.     \({{\text{H}}_{\text{2}}}{\text{PO}}_4^ - \) and \({\text{HPO}}_4^{2 - }\)

D.     HCN and \({{\text{H}}_{\text{2}}}{\text{PO}}_4^ - \)

D