己知：HCN(aq)与NaOH(aq)反应的DH= -12.1kJ/mol；HCl(aq)与NaOH(aq)反应的DH= -55.6kJ/mol。则HCN在水溶液中电离的DH等于

A：-67.7 kJ/mol

B：-43.5 kJ/mol

C：+43.5 kJ/mol

D：+67.7 kJ/mol