Final answer:
The relationship that shows a function is People-Birthdays.
Step-by-step explanation:
A function is a relationship between two sets, where each element in the first set is associated with exactly one element in the second set. In this question, the relationship that shows a function is c) People-Birthdays. This relationship represents a one-to-one mapping between people and their birthdays. Each person has a unique birthday, and each birthday is associated with one person.