A: important
B:more important
C:most important
D:the most important
— There is a photo competition that I want to win.
— _______
用铂作电极电解500 mL含KNO3和Cu(NO3)2的混合溶液一段时间后,在两极均生成11.2L标准状况下的气体,原溶液中Cu2+的物质的量浓度为( )