Answer: 
The correct answer would be option b. domain. 
Explanation: 
Domains are the describe the type of cellular life an organism contain as if they are eukarya, bacteria or archaea domain. Domains are a superkingdom or empire, which is the highest rank or taxon in classification. 
kingdom, class, genus and all other classification taxons are comprising in this domain. The three-domain classification system was introduced by Carl Woese in 1977. 
Thus, the correct answer is option B. domain.