Answer:
I just explained the verticle line test
Explanation:
the verticle line test is if you draw a line at x=(insert x-value in question) and it hits more than two points from that equation then that does not pass the verticle line test. In the picture I attached, the green funtion(circle) does not pass the verticle line test because it hits x=1(black line) in more than one place while the red function(exponential function) passes the verticle line test because it hits x=1 at only one point.