Since a slope differe, this is not linear relationship. Simply, if you connect all points on the graph, they will not lie on the same line. Two next graphs represent the linear relationships, so they represent the linear relationship.
This question is pretty much asking: Write a story that can be represented by the equation y=1.25x.
So, how about this one: Lily's mom tells Lily to clean up her toys. Lily puts toys away at a rate of one toy per every 1.25 seconds.
That's it, simple as that :P
(Sorry if it wasn't too helpful.)
You could use a simple pencil test to figure it out.
Place a pencil vertically on the paper, and move it left to right or vise-versa
When moving it make sure the pencil doesn't hit two points at once if it does it is not a function, but this is not the case
This is a function