Answer:
X
Explanation:
To be a function, the line has to pass the vertical line test. This means that when a vertical line is passed through every x value, it will only cross the graphed line once.
To help: draw vertical lines through each graph.
In graph W: the line would pass through the top and bottom of the circle - not a function
In graph X: the line passes once through every area - a function
In graph Y: the line passes through the top curve as well as the bottom curve - not a function
In graph Z: the line passes through the curves multiple times - not a function