. I asked Peter and ____ of his two sisters, but none of them knew when their uncle came back.

A．either

B．both

C．one

D．Neither

对于关系R，第二范式是要求R中的每一个非主属性满足( )。

A．没有重复的组项

B．只有简单的重复项

C．完全函数依赖于主关键字

D．单值依赖关系