NH₃是重要的化工原料，已知: N₂(g)+O₂(g) ="2NO(g)" ΔH="+a" kJ/mol ①
4NH₃(g)+5O₂(g) =4NO(g)+6H₂O(g) ΔH="-b" kJ/mol ②
2H₂(g)+O₂(g) =2H₂O(g) ΔH="-c" kJ/mol ③
则N₂(g)+3H₂(g) =2NH₃(g)的 ΔH 是

A．(a+0.5b-1.5c)kJ/mol	B．(a-2.5b+1.5c )kJ/mol
C．(2a+3b-2c)kJ/mol	D．(2c+b-a)kJ/mol