Which two statements are true regarding constraints?

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.

Explanation:
Including Constraints
Constraints enforce rules at the table level.
Constraints prevent the deletion of a table if there are dependencies.
The following constraint types are valid:
NOT NULL
UNIQUE
PRIMARY KEY
FOREIGN KEY
CHECK