A:铜和稀硫酸反应:Cu+2H+=Cu2++H2↑
B:NaHCO3溶液与HCl溶液反应:H++HCO3-=CO2↑+H2O
C:铝和硫酸铜溶液的反应Al+Cu2+=Al3++Cu
D:氯化铁滴入沸水中生成氢氧化铁胶体Fe3++3H2O=Fe(OH)3↓+3H+
They ________ carefully, but they didn't ________ anything.