A:少量AlCl3溶液滴入过量的NaOH溶液中:Al3++4OH-= AlO2-+2H2O
B:将一小块金属钠投入到硫酸铜溶液中:2Na+Cu2+=Cu+2Na+
C:FeCl3溶液与Cu反应:Fe3++Cu=Fe2++Cu2+
D:氯气溶解于水:Cl2+H2O2H++Cl-+ClO-
The little boy was ____ ____ so I swam over to save him.
实现下列变化,必须要加入还原剂的是( )