How are vertical lines generally kept in a perspective drawing?

Correct answer: Straight and parallel to one another

In ordinary perspective drawing, vertical lines represent upright edges such as the sides of walls, doors, and buildings. They are generally drawn straight and parallel to one another, especially in a normal eye-level view. Horizontal depth edges may converge toward one or more vanishing points, but upright edges do not normally meet there. Curving or making them horizontal would change the object’s structure, so option D is correct.