Answer:
a. domain
Step-by-step explanation:
Domain is the largest group of organisms. Domain is super kingdom which holds the highest taxonomic rank when it comes to categorize animals. An American microbiologist named Carl Woese et.al. proposed it in 1990.
The three domains are mentioned as under:
1) Bacteria
2) Archaea
3) Eukarya
The organisms in the three domains are classified on the basis of the kind of lipid structure in their plasma membrane, the nucleotide sequences on the rRNA of their cells and their sensitivity towards various antibiotics. The Bacteria and Archaea domians comprise prokaryotic organisms whereas Eukarya domain comprises eukaryotic organisms.
After domain it is kingdom which is the second largest group of organisms in taxonomy.