Which two statements are true about foreign key constraints? (Choose two.)

A.
The columns of one foreign key constraint cannot be used in another foreign key
constraint.

B.
To define a foreign key constraint there must be an associated primary key or unique key
in the same or different table.

C.
The foreign key constraint columns must be defined as NOT NULL.

D.
The foreign key constraint columns must be supported by an index.

E.
The number and data types of foreign key constraint columns must match the parent key.