The unit cell of diamond is composed of:

• A
  $6$ carbon atoms,$4$ forming $ccp$ structure and $2$ occupying half of the octahedral voids.
• B
  $12$ carbon atoms,$4$ forming $ccp$ structure and $8$ occupying tetrahedral voids.
• C
  $8$ carbon atoms,$4$ forming $ccp$ structure and $4$ occupying all octahedral voids.
• D
  $8$ carbon atoms,$4$ forming $ccp$ structure and $4$ occupying half of the tetrahedral voids in an alternate manner.