$Thermococcus$,$Methanococcus$ and $Methanobacterium$ exemplify:

• A
  bacteria whose $DNA$ is relaxed or positively supercoiled but which have a cytoskeleton as well as mitochondria.
• B
  bacteria that contain a cytoskeleton and ribosomes.
• C
  archaebacteria that contain protein homologous to eukaryotic core histones.
• D
  archaebacteria that lack any histones resembling those found in eukaryotes but whose $DNA$ is negatively supercoiled.