A variation is a reference to the differences or deviations, such as the structure and form, as for crossing over is the exchange of genetic material between the non-sister chromatids of the homologous chromosomes during meiosis.
I think the correct answer from the choices listed above is option B. Keratin is the protein in mammals which shows only a primary and secondary structure. Keratin is a fibrous protein forming the structural constituent of hair, feathers, hoofs, claws and many others.
Studies the evolutionary processes that produced the diversity of life on Earth, starting from a single common ancestor.
It's definitely not A. since the toxins would kill butterflies. B. doesn't seem relevant. C. doesn't make sense because the toxins in the pollen are to protect the corn not to make new strains. So, the answer would be D. The carbon dioxide level would increase in the area. Hope this helps!