When graphite is subjected to an electric arc in the presence of an inert atmosphere,it gives:

• A
  $C_{70}$ as main product and $C_{80}$ in small quantities
• B
  $C_{60}$ as main product and $C_{70}$ in small quantities
• C
  $C_{50}$ as main product and $C_{60}$ in small quantities
• D
  equal amounts of $C_{60}$ and $C_{70}$