The depth perception cue employed in the old-fashioned stereoscopes but not
in plain photographs is: (a) variation in color, (b) variation in sharpness, (c) binocular disparity, (d) previous knowledge. (Choose one.)
in plain photographs is: (a) variation in color, (b) variation in sharpness, (c) binocular disparity, (d) previous knowledge. (Choose one.)