let R$1($a$,$ b$,$ c$)$ and R$2($x$,$ y$,$ z$)$ be two relations in which a is the foreign key of R$1$ that refers to the primary key of R$2.$ Consider following four options. $($a$)$Insert into R $1($b$)$Insert into R $2($c$)$Delete from R $1($d$)$Delete from R $2$ Which of the following is correct about the referential integrity constraint with respect to above?