已知：HCN(aq)与NaOH(aq)反应的△H=-12.1kJ·mol^-1；HCl(aq)与NaOH(aq)反应的△H=-55.6kJ·mol^-1。则HCN在水溶液中电离的△H等于（   ）                                                                                    

A．-67.7 kJ·mol^-1

B．-43.5 kJ·mol^-1

C．+43.5 kJ·mol^-1

D．+67.7 kJ·mol^-1