A:2Mg+O22MgO
B:2Al+Fe2O3A12O3+2Fe
C:CaCO3CaO+CO2↑
D:KCl + Ag NO3 ='=' KNO3+AgCl↓
Grace doesn't like math because she thinks it is ________.
下面是关于秦筑长城的诗句,你认为哪个观点比较全面客观