The answer is: The fourth (graph d) represents the function.
The first relation in the image is a function. A function is a relation where each input has exactly one output.
In the first relation, is not a function because it intersects more than once .
The second relation is not a function because , the input 2 has two outputs, so it is not a function.
The third relation is not a function because , the input 3 has no output, so it is not a function.
The fourth relation is a function because the input has one output so it is a function.