Which of the following statements are TRUE concerning referential constraints?

Question $6$Select one or more:

A$.$

A referential constraint includes a foreign key, which is defined in the parent table

B$.$

A referential constraint defines the parent $/$ dependent relationship between tables

C$.$

A referential constraint includes a primary $($or unique$)$ key, which is defined in the dependent table

D$.$

A referential constraint requires an index on the primary $($or unique$)$ key and the foreign key being referenced