Answer:
A, undefined
Step-by-step explanation:
The general rule is that vertical lines are undefined slope, because there's literally no change in x values. The vertical line test also fails, meaning there is no slope. Horizontal lines have a slope of 0, while vertical lines don't own any numbers that are important except for x-axis numbers.
If you do y2-y1 over x2-x1, you literally get 1/0 which is nothing. 0/1 = 0, but 1/0 is nothing.
Hope this helps!
