Because genes control biological traits, because genes have dominant genes and recessive genes, they have dominant and recessive traits. Dominant genes are represented by capital letters, and recessive genes are represented by lowercase letters. There are traits in offspring that parents don't have, and the traits that appear must be recessive. According to the law of gene separation and the mating of two white sheep, their offspring are white sheep and black sheep. It is decided that white is dominant and black is recessive. Because black is recessive, the genome becomes bb, and because the genetic composition of offspring comes from both parents, both parents contain recessive gene B, while parents are dominant, so the genetic composition of parents is Bb and Bb, as shown in the figure:

So choose: C.