化学反应N₂+3H₂=2NH₃的能量变化如图所示，E是正值，该反应的热化学方程式是

A．N2(g)+3H2(g)=2NH3(1)；△H=2(a-b-c)kJ·mol^-1

B．N2(g)+3H2(g)=2NH3(g)；△H=2(b-a)kJ·mol^-1

C．1/2N2(g)+3/2H2(g)=NH3(1)；△H=(b+c-a)kJ·mol^-1

D．1/2N2(g)+3/2H2(g)=NH3(g)；△H=(a+b)kJ·mol^-1