A. Objects that are far away appear smaller than they really are.
B. The land and the sky always appear to meet at the horizon.
C. The artist's eye level is the viewpoint from which everybody else views the picture.
A. Objects that are far away appear smaller than they really are
From the Encyclopedia Britannica
The three components essential to the linear perspective system are orthogonals (parallel lines), the horizon line, and a vanishing point. So as to appear farther from the viewer, objects in the compositions are rendered increasingly smaller as they near the vanishing point.