One Proximate Factor Related to Ultraviolet Vision in Zebra Finches

One proximate factor related to ultraviolet vision in zebra finches (Taeniopygia guttata) involves:

A) changes in the curvature of the lens, which helps to filter out certain wavelengths of light.
B) a single amino acid change that alters pigment characteristics.
C) alterations to retinal structure that inhibit processing of violet pigments.
D) hormones that trigger the release of ultraviolet pigments from specific brain regions.
E) a vast number of genetic substitutions, the effects of which have yet to be quantified.