Which two statements are true regarding constraints? (Choose two.)
A.
A foreign key cannot contain NULL values.
B.
A column with the UNIQUE constraint can contain NULL values.
C.
A constraint is enforced only for the INSERT operation on a table.
D.
A constraint can be disabled even if the constraint column contains data.
E.
All constraints can be defined at the column level as well as the table level.
B, D