Much to ________ surprise of the students, the concert which was held once a year turned out to be ________ complete failure.

A．/; a

B．the; a

C．the; /

D．/; /

如图4－10为各烧杯中通电后，观察到Cu溶解，下列说法正确的是(   )

A．a是正极

B．a是负极

C．Pt极上产生气体的物质的量是Fe极的2倍

D．Q池CuSO₄溶液溶质的质量分数不变

图4－10