The correct option is C Methanogens
Archaebacteria live in harsh habitats. Some archaebacteria live in marshy areas and also in the gut of the ruminants. These are referred to as methanogens. They produce methane gas or biogas.
Some archaebacteria are salt loving so called halophiles. Those which live in acidic conditions are called acidophiles. Cryophiles are archaebacteria which survive extreme cold conditons.