Hello! There are a few things that determine whether or not something is a function. In this case, to determine whether a relation is a function, we look at the domains, which are the x-coordinates, the first number of the pair. If the number occurs in the x-coordinate for more than one pair in a relation, then it's not a function. If a number only occurs as an x-coordinate once in the relation, then it's a function. In other words, they each have only one y-coordinate in the relation. For this question, the first, second, and third relations are functions. The fourth one is not a function, because the 3 has more than one y-coordinate, so it occurs as an x-coordinate more than once. Here are the answers easier to read.
