I ______ her, but I never could.

A．ought to help

B．must help

C．ought to have helped

D．must have helped

已知：Fe₂O₃ (s)＋C(s)= CO₂(g)＋2Fe(s)   △H=234.1kJ·mol^－1

C(s)＋O₂(g)=CO₂(g)   △H=－393.5kJ·mol^－1 , 

则 2Fe(s)＋O₂(g)=Fe₂O₃(s)的△H是(       )

A．－824.4kJ·mol^{－ 1}

B．－627.6kJ·mol^－1

C．－744.7kJ·mol^－1

D．－169.4kJ·mol^－1