(A)FeCl2heat→FeCl3heat,air→FeCl2Zn→Fe(B)FeO2heat→Fe3O4CO,600∘C→FeOCO,700∘C→Fe(C)FedilH2SO4→FeSO4H2SO4,O2→Fe(SO4)3heat→Fe(D)FeO2heat→FeOdilH2SO4→FeSO4heat→Fe