Which group includes organisms like methanogens that can thrive in extreme environments?

The correct choice is rooted in the characteristics that define Archaea, particularly their ability to thrive in extreme environments. Methanogens are a specific type of Archaea that produce methane as a metabolic byproduct and are often found in habitats such as swamps, marshes, and the guts of animals, which are harsh and anaerobic conditions.

Archaea possess unique cell membrane structures and biochemistry that allow them to withstand extreme temperatures, salinity, and acidity, distinguishing them from Bacteria and Eukarya. While Bacteria also include many diverse groups, they do not specifically encompass the methanogenic organisms found in extreme environments. Eukarya generally includes organisms such as plants, animals, and fungi, which typically do not thrive in such extreme conditions. Fungi are also not associated with extreme environments like those inhabited by methanogens. Thus, the defining characteristics of Archaea make them the appropriate group for organisms like methanogens.