When one$-$to$-$one relationship in E$-$R model is mapped into relational data model, the one$-$to$-$one relationship is generally represented as

Group of answer choices

c$.$ a pair of primary key $($in one table$)$ and a foreign key $($in another table or the same table$),$

b$.$ a foreign key

a$.$ a primary key

d$.$ a new table with a pair of foreign keys, each of which is associated with or references to the primary key in its parent table.