Why have some microbiologists proposed using ribosomal RNA as the basis for defining bacterial species?

A) Ribosomal RNAs are highly conserved genetic sequences present in all prokaryotes.
B) the "interbreeding population" criterion does not apply to bacteria.
C) ribosomal RNA is the basis for domain assignment.
D) bacteria vary too little in their physical and biochemical traits.
E) bacteria are not interbreeding populations, and ribosomal RNAs are highly conserved genes present in all prokaryotes.