已知K时下列热化学方程式：①NH(g)→N(g)+H(g)△rHmΘ=.kJ·mol－②H(g)+/O(g)→HO(g)△rHmΘ=.kJ·mol－③NH(g)+O(g)→NO(g)+HO(g)△rHmΘ=.kJ·mol－试确定△fHmΘ（NH，g，k）=()kJ·mol－A.B.C.D