$8)$ Assume that the following functional dependencies are simultaneously satisfied by a relation r$($R$)$:

$\{$A$,$B$\}->\{$C$\}$

$\{$C$\}->\{$D$\}$

$\{$D$\}->\{$A$\}$

What are the candidate keys of this relation?

Group of answer choices

a$)\{$A$,$B$\},\{$C$,$D$\},$ and $\{$A$,$D$\}$

b$)\{$A$,$B$\}$ and $\{$C$,$D$\}$

c$)\{$A$,$B$\}$ and $\{$D$,$B$\}$

d$)\{$C$,$D$\}$