The correct option is C tertiary consumers
Ecological pyramids or Eltonian pyramids were made by Charles Elton. Trophic levels are shown as a stack/block. The size of the block is proportional to energy/biomass/number of organisms present. Base of ecological pyramids are producers which are the energy factories of ecosystem and repositories of all energy in an ecosystem. Hence, they are the base of the pyramid since they capture the solar energy and convert it into chemical energy. In further trophic levels, the energy decrease due to the 10% law. The apex of the pyramid have tertiary consumers with least amount of reserved energy.