A relation has four fields: A$,$ B$,$ C$,$ and D$,$ where AB is the only key. What normal form $(3$NF$,$ BCNF or neither$)$ is the relation in if

a$)$ A$,$ B$,$ C$,$ D are each functionally dependent on AB$?($i$.$e$.,$ AB$->$A$,$ AB$->$B$,$ AB$->$C$,$ AB$->$D$)$

b$)$ A$,$ B$,$ C$,$ D are each functionally dependent on AB$,$ while D is functionally dependent on C$?$

c$)$ A$,$ B$,$ C$,$ D are each functionally dependent on AB$,$ while D is functionally dependent on B$?$

d$)$ A$,$ B$,$ C$,$ D are each functionally dependent on AB$,$ while B is functionally dependent on C$?$