Answer : The correct answer is- c.dissimilar then scientists thought.
The three-domain system recognizes basic differences that are present with two groups of prokaryotes, which are archaebacteria and eubacteria.
According to this system, life forms are divided into three distinct domains that are Archaebacteria, eubacteria and Eukarya based on the differences in the rRNA (ribosomal RNA) sequences, lipid structure in their cell membrane, and antibiotic sensitivity.
This system of classification arose when scientist found that the eubacteria and archaebacteria were more than they thought.
For instance, archaebacteria are single celled microscopic prokaryotes that mainly live in harsh environmental conditions (like hot springs) whereas eubacteria do not live in such conditions.