---Have all the mysteries been cleared up?

--- Almost. But ______ only one question ______.

A．there remains; answered

B．it remains; to be answered

C．there remains; to be answered

D．it remains; answered

用两根铂丝做电极插入KOH溶液中，再向两个电极上分别通甲烷气和氧气可形成原电池——燃料电池，根据两极反应的实质判断，

的一极，在下列叙述中正确的是                                   

A．阴极：4H2O+2O2+8e=8OH-

B．正极：4H2O+2O2+8e=8OH-

C．阴极：4OH--4e=2H2O+O2↑

D．正极：4OH--4e=2H2O+O2↑