(Choose 1 answer)
When does the Central visual ray appear at the observer's eye level plane?
A. When the observer looks up. The central visual ray points horizontally (parallel to the gro lies exactly on the eye level plane.
B. When the observer looks down. The central visual ray points horizontally (parallel to the c therefore lies exactly on the eye level plane.
C. When the observer looks straight. The central visual ray points horizontally (parallel to the therefore lies exactly on the eye level plane.
D. When the observer looks around. The central visual ray points horizontally (parallel to the therefore lies exactly on the eye level plane.
