Answer: D. Yes because it passes the vertical line test.
Explanation
A function cannot have duplicate x-coordinates.
When given a table or a set of coordinates, if there is an x-coordinate that is paired with two different y-coordinates then it is not a function.
When given a graph, the simplest way to determine if it is a function is to use the vertical line test. If you can draw a vertical line anywhere through the graph and it passes through two points, then it is not a function.
In the given graph, it passes the vertical line test so it IS a function.