Relation is not function if any same x-values has at least two different y-values
It is not A because x-value 2 has two y-values 3 and 1.
It is not B because x-value 3 has two y-values 3 and 2.
It is not D because x-value 1 has two y-values -1 and -2.
Answer is C.
Hope this helps.
