If you are joining 2 tables in a relational database and elect to enforce referential integrity, which of the following would cause an error?

A. The primary keys of each table are different

B. There are entries in the foreign key of the table being joined that don't exist in the primary key of the other table.

C. There are entries in the primary key of the table being joined that don't exist in the foreign key of the other table.

D. The secondary key of the table being joined does not match the primary key of the other table.