The statement "A vertical line is parallel to the y-axis" is always true.
1. By definition, a vertical line runs up and down, perpendicular to the horizontal plane.
2. The y-axis in a standard Cartesian coordinate system is also a vertical line.
3. Two lines that run in the exact same direction and never intersect are considered parallel.
4. Therefore, any vertical line in the Cartesian plane will never intersect with the y-axis (unless it is the y-axis itself).
5. Hence, a vertical line is always parallel to the y-axis.