Which of the following represents a function? explain too i don’t understand this.

Im pretty sure its C because in a function, the X value can with two Y values. for example you can have (3, -5) and (3, 0) but you cant have the Y being the same one for two points which would be like (3, -5) and 6, 5)
im really bad at explaining but thats the simplest way i learned