When defining a foreign key on a table, which statement is true?

A.
It is not mandatory to have an index on the foreign key columns but it can help to avoid locking
problems.

B.
There is no need to define an index on the foreign key columns as DB2 cannot use an index for
foreign key checking.

C.
It is not mandatory to have an index on the foreign key columns but it can help performance
when you insert rows into this table.

D.
You must define an index on the foreign key columns where the index columns are the same as
the foreign key columns to guarantee
uniqueness of the foreign key.

Explanation: