Answer: A. Archaea
Domain Archaea is the group of single celled prokaryotic organisms. These organisms lack a well defined nucleus and cell organelles. The cell wall of these organisms lack peptidoglycan which makes them distinct from bacteria. These organisms are tolerant to saline conditions and they survive in marshes, hence they are called as halophiles. They produce methane as a metabolic byproduct, therefore are called as methanogens.