For relation schema R$($A$,$B$,$C$,$D$,$E$,$F$)$ AND DEPENDANCE SET F$\{$D$->$BE$,$E$->$AF$,$F$->$CD$,$AEF$->>$BCD$\}.$GIVE DEFINITION OF KEY AND DEFINE THE POSIBBLE KEYS WITH ARGUMENTATION. IN WHICH NORMAL FORM IS R $-$ DEFINE THE FORM AND GIVE ARGUMENTATION WHY R IS IN THIS FORM? IF IT IS IN LOWER THAN $3$ NF NORMALIZE TO $3$NF