Thermococcus, Methanococcus and Methanobacterium exemplify

• A

  Bacteria that contain a cytoskeleton and ribosomes
• B

  Archaebacteria that contain protein homologous to eukaryotic core histones
• Correct answer
  C

  Archaebacteria that lack any histones resembling those found in eukaryoties but whose DNA is negatively supercoiled
• D

  Bacteria whose DNA is relaxed or positively supercoiled but which have a cytoskeleton as well as mitochondria

Hence, the correct answer is option: 'C'.