Answer:
The first graph is the only one who is not a function
Explanation:
Functions
The condition that a relation between x and y must fulfill to be called a function is that for each value of x, there is one and only one value for y.
That is easy to spot by taking an imaginary vertical line and having is slipped through all of the domain. If the line touches more than once (or never touches) the graph for all the values of x, it's not a function.
Checking on the first graph, we can see it's the only one who has the above-mentioned description. In fact, for a specific value of x, there are infinitely many values of y. The rest of the graphs touches our imaginary line only once per value of x, thus:
The first graph is the only one who is not a function