Depth is the
a. apparent distance from front to back in a piece of artwork.
b. distance or area between, around, above, below, and within objects.
c. degree to which the surface of an object seems to have a particular feel.
d. area of dark created when an object blocks light

A

Explanation:

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photography had emerged as an elite art pursued by a few creative individuals for a few wealthy patrons. but now, said bauldelaire, it was succumbing to "the great industrial madness of our times." it was becoming a mass production industry that catered to middle-class tastes, including a taste for gadgetry. the stereoscope, the first 3d imaging system, had turned looking at photographs into parlor entertainment. a "thousand hungry eyes were bending over the peepholes of the stereoscope as though they were the attic-windows of the infinite.