Choose the highest ranked category, which includes the greatest number of organisms.

The highest ranked category or the highest taxonomic rank of organisms is a domain. Carl Woese designed three-domain system of taxonomy which includes Eukarya, Bacteria and Archea, and they differ in rRNA. The first includes all living organisms that have a nucleus and membrane-bound organelles and multicellular organisms. Other two are prokaryotic microorganisms or single-celled organisms whose cells have no nucleus.