48. 下列哪一種化學反應是氧化還原反應?(A) Na2SO3+H2SO4 → Na2SO4+H2O+SO2(B) CH3CHO+2Cu(OH)2 → CH3COOH+Cu2O+2H2O(C) CaCO3+2HCl → CO2+H2O+2CaCl2(D) BaCl2+H2SO4 → BaSO4+2HCl