Ans. (D). Archaebacteria.
Archaebacteria or archaea make a domain of single-celled, prokaryotic organisms. These organisms were the first living organisms with simple, primitive cells, having no true nucleus and other membrane-bound organelles.
These organisms had tolerance for extreme environmental conditions, such as salt lakes and hot springs, where other life-forms could not survive.
Thus, the correct answer is option (D).
