Answer:
The answer to your question is: the third graph
Step-by-step explanation:
To test if a relation is a function you need to draw a vertical line in different areas of the graph (vertical line test), if this line cuts the curve in two or more points, it is not a function.
After doing this test in the graphs, we notice that in graphs 1 and 2 the vertical line cuts the graph in two points so the are not functions.
The forth graph is a vertical line.
Only the third graph is cut in one point.
See the test in the attachment.
