5) The fields or field on which an index is built is called the primary key. a. True b. False 6) The index key always consists of only one field in the table. a. True b. False 7) Security is the prevention of unauthorized access to the database. a. True b. False 8) Entity integrity is the rule that no field that is part of the primary key may accept null values. a. True b. False 9) Referential integrity is the rule that if table A contains a foreign key that matches the primary key of table B, the values of this foreign key must either match the value of the primary key for some row in table B or be null. a. True b. False 10) Legal-values integrity is the set of rules that governs the values allowed in a field. a. True b. False