A way that I use to determine if something is a function or not is to ask whether or now it passes the “vertical line test”. In other words, does an x have two y’s? if we graphed these points, and proceeded to draw a vertical line through it, if it touches the function twice, then it is not a function. So I believe your answers would be A and C (In A, when x is 2, there are two y’s. Same goes with C, when x is 1, 4, 9 etc).
I hope this answer helps! :)
