Pax-6 usually causes the production of a type of light-receptor pigment. In vertebrate eyes, through, a different gene (the rh gene family) is responsible for the light-receptor pigments of the retina. The m gene, like Pax-6, is ancient. In the marine ragworm, for example, the rh gene causes production of c-opsin, which helps regulate the worm's biological clock. Which of these most likely vertebrate vision? A) In animals more ancient than ragworms, the rh gene(s) coded for visual receptor pigments; in lineages more recent than ragworms, rh has flip-flopped several times between producing biological clock opsins and visual receptor pigments. B) The Pax-6 gene mutated the rh gene among early mammals. C) During vertebrate evolution, the rh gene for biological opsin was co-opted as a gene for visual receptor pigments. D) Pax-6 was lost from the mammalian genome and replaced by the rh gene much later.