DCM色散补偿模块实际上是具有（）的光纤

Suppose we have the relation schema R(A,B,C,D) with functional dependencies ;F{A→ B,B→C,C→D,D→A},then R(A,B,C,D) at least is in

A．1NF

B．2NF

C．3NF

D．BCNF