What does the keystone do?
A. Supports the downward and outward thrust of the rounded arch
B. Is a decorative element of the rounded arch
C. Is necessary for a door in a rounded arch
D. Supports the weight of the rounded arch

To create an illustration of perspective, this artist did all of the following except 1) show clear orthogonal lines 2) have an implied vanishing point 3) distort proportion to keep the background and foreground the same size 4) include value changes between the foreground and background i was thinking maybe 1