Answer:
Third graph does not represent a function.
Explanation:
A function is a relation in which each element of the domain corresponds with exactly one element of the range. You could use the vertical line test to verify whether a given graph represents a function. The vertical-line test states if a vertical line passes through more than one point on the graph of a relation, then the relation is not a function. A relation is a set of pairs of input (x values) and output (y values).
Looking at the third graph and conducting the vertical line test, you'll see that the vertical line will pass through more than one point on the graph of a relation.
Below is a screen capture of the vertical line test I've done using the image you've provided. You'll see that given an x-value of 3, it has two corresponding y-values: 4 and -4.