The correct option is D Taxon
A taxon is the category or unit of classification, such as kingdom, class, species. Each level or step in the taxonomic hierarchy is also called a category.
Kingdom is the largest category while species is the smallest.
Genus is a category composed of a group of related species. An example is the genus Solanum, which includes many related species such as S. lycopersicum (tomato) and S. tuberosum (potato).