The UNIQUE Constraint Differs from the PRIMARY KEY Constraint in What

Multiple Choice

The UNIQUE constraint differs from the PRIMARY KEY constraint in what way?​

A) ​The UNIQUE constraint does not allow NULL values.
B) ​The UNIQUE constraint can be created at either the column level or the table level.
C) ​The UNIQUE constraint allows NULL values.
D) ​The UNIQUE constraint ensures that a specific condition is true before a data value is added to a table.