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Which of the following is not a basic requirement of a relational database?
A.
Every column in a row must be single valued.
B.
Primary keys cannot be null.
C.
Foreign keys, if not null, must have values that correspond to the value of another foreign key in another table.
D.
All nonkey attributes in a table should describe a characteristic about the object identified by the primary key.
E.
All of the above are basic requirements of a relational database.