Why do humans genetically modify organisms, especially crops that produce important food items that we rely on for nutrients?

the answer is d.) homologous; have mammary glands

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".

i think the answer is a.keratin is the pigment responsible for skin color.