Lightness constancy is most clearly facilitated by

A) proximity.
B) interposition.
C) relative luminance.
D) retinal disparity.

Lightness constancy refers to the ability of the visual system to perceive the relative lightness of objects as remaining constant despite changes in lighting conditions. This is most clearly facilitated by perceived relative luminance, which takes into account the amount of light reflected by an object relative to its surroundings. Proximity and interposition can help with depth perception, while retinal disparity is important for perceiving depth and spatial relationships between objects, but none of these factors play as significant a role in facilitating lightness constancy as relative luminance.