(1) Xiaoming thinks that A can be a solid. In the displacement reaction, the reactant is hydrogen, so it is the reaction of hydrogen reducing copper oxide and iron oxide. This place requires us to write reaction II, not the substitution reaction just analyzed, so the answer is: Cu, 2H2+O2? Light it? . ? 2H2O

(2) Xiaohong thinks it is a nonmetallic solid. Through the above analysis, we know that A is carbon and E is oxygen, but the equation written this time is I, that is, A+B=C+D, so the answer is: O2, C+2CuO? High temperature? . ? 2Cu+CO2↑；

(3) Xiaohua thinks that A can be a metal solid. According to the above analysis, it can be a reaction in which metals participate and reflect metal activity, but it must react with hydrochloric acid or metal chloride (or sulfuric acid or corresponding soluble sulfate). So it can be written that A can react with hydrochloric acid solution or metal chloride (or sulfuric acid or corresponding soluble sulfate). So the answer is: Zn+CuCl2 θ ZnCl2+Cu. (or Zn+2.