Which statement about NOT ENFORCED unique constraints is TRUE?

A.
NOT ENFORCED unique constraints can not be defined on primary key columns

B.
The query optimizer will consider a NOT ENFORCED unique constraint when selecting an optimal data
access plan

C.
When attempting to insert data that does not conform to a NOT ENFORCED unique constraint, a warning
will be returned

D.
Storage requirements for a NOT ENFORCED unique constraint are no different than the storage
requirements for a similar unique index