CUSTOMER In table CUSTOMER, CID is the primary key (Customer ID). RENTALS In the table RENTALS, RTN provides the rental number (the primary key), CID is the customer's unique id, PICKUP is the city where the car was picked up, and Return is the city where the car was returned. RENTCOST RENTCOST shows the base cost of renting a given MAKE for one day. CITYADJ If the return city of table RENTALS is the one listed in table CITYADJ, the cost of the rental is multiplied by FACTOR and by DAYS shown in table RENTLENGTH below. RENTLENGTH RENTLENGTH shows the number of days for the rental number (RTN) shown in table RENTALS. In a database used in reality, this table would be merged with the RENTALS table. SELECT CID FROM RENTALS GROUP BY CID HAVING COUNT (DISTINCT MAKE) = (SELECT COUNT(*) FROM RENTCOST) The operation performed by this query is:

A difference

A division

A union

A join