Each of the points take the form (x,y), where x and y represent the coordinates of the points on the xy-plane. A function means a plot that doesn't have several y-values for a single x-value.
In choice 1, there are not two points with the same x value and different y value; thus, this relation is a function.
Choices 2, 3, and 4 all have points with the same x value, but different y value. Thus, these relations are not functions.
Let me know if you need any clarifications, thanks!
