The first two graphs are of functions (line, parabola). The last two graphs (absolute value, circle) are not of functions.
Step-by-step explanation:
If a vertical line can be drawn that intersects the graph in 2 or more places, then the graph is <em>not</em> that of a function. (This is called "the vertical line test.")
The last two offered graphs will intersect some vertical lines in 2 places, so are not a function.