Purebred dogs are first assigned the same litter number until they are individually registered with a name. then the dogs will be assigned a unique registration number with a dog registry. many people choose to have a microchip implanted in the dog so that it can be read to immediately find the dog's owner.

which of the following relations is not a function?

a. (registration number, litter number)

b. (microchip number, registration number)

c. (litter number, microchip number)

d. (microchip number, litter number)