Which statement regarding NOT ENFORCED unique constraints is true?
A. NOT ENFORCED unique constraints enforce uniqueness only for primary key columns.
B. The query optimizer will consider a NOT ENFORCED unique constraint when selecting the optimal data access plan.
C. Storage requirements for NOT ENFORCED unique constraints are identical to storage requirements for a unique index.
D. When attempting to insert data that does not conform to the NOT ENFORCED unique constraint, an error will be returned and the record will not be inserted.