$R=\{A,B,C,D,E,F\}$

ABC$>D,$ and $D>E,$ and $E>F$

Transform $R$ to $3$NF$.$

$R1=\{A,B,C,D\}$ with $PK=\{A,B,C\}$

$R2=\{D,E\}$ with $PK=\{D\}$

$R3=\{E,F\}$ with $PK=\{E\}$

$R1=\{A,B,C,D\}$ with $PK=\{A\}$

$R2=\{D,E\}$ with $PK=\{D\}$

$R3=\{E,F\}$ with $PK=\{E\}$

$R1=\{A,B,C,D\}$ with $PK=\{A,B\}$

$R2=\{D,E\}$ with $PK=\{D\}$

$R3=\{E,F\}$ with $PK=\{E\}$

$R1=\{A,B,C,D,E\}$ with $PK=\{A,B,C,D\}$

$R2=\{E,F\}$ with $PK=\{E\}$