The fourth set of ordered pairs is the function.
The definition of a function is that no matter what x value you put in, you get only one y value out. So no x value will have more than one answer. However, in the first 3 choices, you can see that each one has an x value that has two different y value answers.
In grouping 1, x = -1 gives us both y = 1 and y = -1.
In grouping 2, x = 0 gives us both y = 1/2 and y = 3/4.
And in grouping 3, x = -2 gives us both y = 1 and y = 2.
Therefore, the last grouping is your function.
