Ans.
According to modern classification system, all organisms can be divided into three domains (archaea, bacteria, and eukarya) and six kingdoms (archaebacteria, eubateria, protista, fungi, plantae, and animalia.
Organisms are grouped into these domains or kingdoms on the basis of common characteristics, such as cell type (prokaryotic or eukaryotic), mode of reproduction (sexual or asexual), nutrient acquisition (autotrophic or heterotrophic).
Thus, the correct answer is option). 'three domains and six kingdoms.'