For a relation to be a function, it can only have 1 of each number as an X value. If there are 2 or more identical X values it cannot be a function. The X value is the first value inside the parenthesis. (X,Y)
A has 2 3's as an X value so cannot be a function. B has 2 2's as an X value so cannot be a function. C has no multiple X values so is a function. D has 2 -2's as an X value so cannot be a function.