When determining the different between x and y and if they have a linear relationship, is the way in which the points are presented. If the points seem to form in a similar pattern, going in a line, then its likely to be linear. If it seems to form a strange shape (that is not a line), then it is nonlinear.
On graphs F, H, and G, the dots all seem to be going in a line, (G and H are going diagonal, F going horizontal), however J seems to form a line but then randomly goes vertical. This means that J is the nonlinear choice as it does not make a line from one side of the graph to the other.
