How are human beings (and other animals) so easily able to focus on visual stimuli at different distances? select one: a. the cornea changes its level of transparency depending on what one is seeing. b. different photoreceptors in the retina, specifically rods and cones, are activated by stimuli at different distances. c. the lens can accommodate by change its shape in order of focus nearer or faraway objects. d. when we view objects at different ranges, the overall shape of the entire eyeball changes microscopically.