Answer: species.
- A species
- B variety
- C strain
- D clone
Correct answer: A. species
Explanation: Species is the lowest rank, sitting just below genus.
The taxonomic hierarchy narrows from Kingdom (broadest, covering the most organisms but fewest shared traits) down to Species (narrowest, fewest organisms but most shared traits) - every level in between is a progressively more specific subset of the one above it.
Concept context
Biodiversity, taxonomy, binomial nomenclature, the taxonomic hierarchy, and taxonomic aids like herbaria and botanical gardens. The foundational first chapter of NCERT Biology.