2+ -A Zn +2OH ==Zn(OH)2下箭头 →ZnCO3+2NaOH==Zn(OH)2下箭头+Na2CO3 2+ 2-B Ba +SO4 ==BaSO4下箭头 →Ba(OH)2+H2SO4==BaSO4下箭头 +2H2OC 省略 2+ 2+D Cu+2Ag ==Cu +2Ag下箭头 → Cu+2AgCl==2Ag+ CuCl2P8