Which is an example of a higher-order invariant in size constancy?

A) the size of an object's retinal image
B) the actual size of the image out in the world
C) the apparent size of the object as the subject perceives it
D) the ratio between the retinal size of the object and the retinal size of a stimulus in the background

The ratio between the retinal size of the object and the retinal size of a stimulus in the background is an example of a higher-order invariant in size constancy because it takes into account the relative size of the object in comparison to other objects in the environment, rather than just the object's retinal image or actual size.