Let's check by calculating their slopes. All three horizontal lines have a slope of 0, so they must all be parallel. In fact, every horizontal line has a slope of 0. Since a horizontal line never moves up or down, its y-coordinates never change. When we divide by the change in x-coordinates to find slope, our final answer will be 0.
Vertical lines go straight up and down.
Here is a picture of a vertical line. In this picture, Joan's tongue is also vertical. Joan's tongue and the green line look parallel. In fact, like horizontal lines, vertical lines are always parallel to each other. Let's try to calculate the slope of the green line.