Let X$\{$w$,$v$,$u$\}$ represents a relation $($table$)$ with name X and fields w$,$ v$,$ and u$,$ where the field w $($underlined$)$ is the primary key for X$.$

Let us assume also that data entity A has attributes $\{$a$,$ b$,$ c$\},$ a is the key attribute, B has attributes $\{$x$,$ y$,$ z$\},$ x is the key attribute, and the relationship R has attribute $\{$r$\}.$

Which of the following fragments of a relational model represent the correct mapping of the given fragment of E$-$R diagram?

a$)$ A$\{$a$,$ b$,$ c$\}$; B$\{$x$,$ y$,$ z$\}$; R$\{$a$->$A$.$a$,$ x$->$B$.$x$,$ r$\}$

b$)$ A$\{$a$,$ b$,$ c$\}$; B$\{$a$->$A$.$a$,$ x$->$B$.$x$,$ y$,$ z$,$ r$\}$

c$)$ A$\{$a$,$ b$,$ c$\}$; B$\{$x$,$ y$,$ z$,$ a$->$A$.$a$,$ r$\}$

d$)$ A$\{$a$,$ b$,$ c$,$ x$->$B$.$x$,$ r$\}$; B$\{$x$,$ y$,$ z$\}$