The correct option is
C Monocarpellary
Poaceae or Gramineae is a large family of monocotyledonous flowering plants which are collectively referred to as grasses. In Poaceae, the gynoecium is monocarpellary, ovary superior, unilocular with a single ovule, basal placentation, style short, stigma (usually 2 )feathery, papillate or branched.
So, the correct answer is 'Monocarpellary'.