How could you genetically modify an animal so that it would distinguish more shades of green?

A) Introduce genes for different opsins that respond in the green region of the spectrum.
B) Introduce genes to produce green fluid in the eyeball, because green fluids will not absorb green light.
C) Induce genes to produce a greater number of cone cells in the fovea.
D) Induce increased production of cGMP to increase opening of cGMP- gated sodium channels.