What is the use of Referential Integrity in MS Access?

a. It allow to enter a value in the foreign key field of a child table if that value exist in the primary key of the parent table
b. It does not allow to enter a value in the foreign key field of a child table if that value exist in the primary key of the parent table     
c. It allow to enter a value in the Primary key field of a child table if that value exist in the Foreign key of the parent table
d. None of above

Ans: A