Consider a relational schema $S=(U,V,W,X,Y,Z)$ on which the following functional dependencies hold:
$(U \rightarrow V, VW \rightarrow X, Y \rightarrow W, X \rightarrow U)$
Which are the candidate keys among following options?
- $UY, VY$
- $UY, VY, XY$
- $UYZ, VYZ, VWZ$
- $UYZ, VYZ, XYZ$