$RuBisCO$ and $Collagen$ are the most abundant proteins in the living world.

• A
  $PEPcase$ of plants and $Keratin$ of animals
• B
  $Ribozyme$ of plants and $Collagen$ of animals
• C
  $Alcohol \text{ } dehydrogenase$ of plants and $Melanin$ of animals
• D
  $RuBisCO$ of plants and $Collagen$ of animals