anything,nothing,no one的谓语动词也就是be+anything,nothing,no one时,be 为什么?

问题描述:

anything,nothing,no one的谓语动词
也就是be+anything,nothing,no one时,be 为什么?

这是规定

is/was

anything,nothing,no one的谓语动词用单数.
现在时态是is
过去是 was
还有has been之类的形式