The most abundant microorganism are: -
Bacteria
The correct option is B.
Explanation of the correct option: -
Explanation of the incorrect options:-
Option A: -
A virus is a submicroscopic infectious agent that replicates only within an organism's live cells. Viruses infect all living things, including bacteria and archaea, from mammals and plants to microbes.
Option C: -
Option D:-
Hence most abundant microorganisms are bacteria.