Which graph does not represent a function?

On a coordinate plane, a curved crosses the y-axis 1 time and the x-axis 2 times.

On a coordinate plane, a straight line with a negative slope crosses the y-axis 1 time and the x-axis 1 time.

On a coordinate plane, an oval line crosses the y-axis 2 times and the x-axis two times.

On a coordinate plane, a line with an s curve crosses the y-axis 1 time and the x-axis 1 time.