Which of the following is NOT one of the eight hierarchical categories in modern biological classification?

The correct answer is "C. Tribe" because it is not one of the primary hierarchical categories used in the formal system of biological classification. The eight main taxonomic ranks in modern biological classification include Kingdom, Phylum, Class, Order, Family, Genus, Species, and Domain.

While "Tribe" does exist as a ranking in some classification systems, particularly within the context of plants and animals, it is a subordinate category to "Family" and is not recognized as one of the primary eight levels used universally across all organisms. "Domän" and the other categories listed are fundamental to our understanding of biological diversity, as they provide a structured approach to classify and comprehend the relationships among living organisms.