阶梯式电价方案将居民用电实行分档定价，用电越少价格越低，用电越多价格越高。居民用电价格应该由    决定。

A．居民的收入水平

B．社会必要劳动时间

C．供求关系

D．居民的用电量

．I really don’t know _______I kept the secret papers．

A．where was it

B．it was where that

C．where it was that

D．where was it that