Iwill give brainliest to whoever is correct.

Use the vertical line test.
Think of a vertical line moving from left to right across the graph.
If the line touches more than one point on the graph at a time, it is NOT a function.
If the vertical line touches at most one piont ion the graph, then it is a function.

Look at the circle, on the top right.
As the vertical line moves to the right, it will touch two points of the circle; therefore, the circle is not a function.

Only one graph passes the vertical line test, and it is the bottom right graph.

Only the fourth graph, in the lower right-hand corner, represents a function.  Note that in this graph, there is exactly one y-value for every x-value.

If there is more than 1 y value for any given x-value, you've got a relationship, not a function.