Anewly made car will have a model number, a parts number, and a serial number. a model number is assigned by the manufacturer to identify each type of car. a parts number identifies one part of the smaller parts that make up the car. a serial number is unique to each car produced and identifies it.

which relation is a function?

(parts number, serial number)
(model number, parts number)
(serial number, model number)
(serial number, part number)