When the values in one or more attributes being used as a foreign key must exist in another set of one or more attributes in another table, we have created a(n):

ANS:C - referential integrity constraint.

Referential integrity is a database concept that ensures that relationships between tables remain consistent. When one table has a foreign key to another table, the concept of referential integrity states that you may not add a record to the table that contains the foreign key unless there is a corresponding record in the linked table.