Choose the correct option regarding the diversity of prokaryotes.

• A
  The number of prokaryotic species is not known with certainty.
• B
  Conventional taxonomic methods are not suitable for identifying microbial species,and many species cannot be cultured in the laboratory.
• C
  If biochemical or molecular criteria are used for defining prokaryotic species,their diversity alone might run into millions.
• D
  All of the above.