Which of the following best describes a database view?
A. The dynamic result of one or more relational opertaions operating on the base relations to produce another relation.
B. Additional rules specified by the users or database administrators of a database that define or constrain some aspect of the enterprise.
C. In a base relation, no attribute of a primary key can be null.
D. The candidate key that s selected to identify tuples uniquely within the relation.