B. sexual selection, which alters allele frequencies in the gene pool.
The condensation of water vapor formed the early oceans. It is an important part of the water cycle. It is easy to eliminate the other answers in this question. It can't be meteorites, living organisms, or nitrogen.
Essentially traits of both genes will be shown. Take heterochromia for example, where a person has a green eye and a blue eye, both have some part in developing a trait.
