Function is a specific kind of relation, where relation is a collection of ordered pairs where there you have (x, y) related, just as it is in the graph presented. In the more general case, relation can have many ordered pairs where one of the X are related to many Y, lets say Y1, Y2, Y3, and it is possible to have: (x, y1), (x, y2), (x, y3), and it is ok.
In the other hand, function is the specific case where for each value of X there in only one value of Y. It means: (X1, Y1) , (X2, Y2) , (X3, Y3), and so on.
In the present case, for X = 0 it appears to have 3 different values of Y, and for this reason it is a relation, but not a function.
From the solution developed above we are able to say that the presented graph represents A. a relation but not a function.