The correct answer is: A. Pyramid of energy.
A pyramid of energy is a graphical representation that shows the amount of energy that is transferred from one trophic level to the next in a food chain. The pyramid of energy is always upright because energy is always lost as heat at each trophic level. This means that the amount of energy available to organisms at higher trophic levels is always less than the amount of energy available to organisms at lower trophic levels.
A pyramid of number is a graphical representation that shows the number of organisms at each trophic level in a food chain. The pyramid of number can be upright or inverted, depending on the ecosystem. In an ecosystem with a large number of primary producers, such as a grassland, the pyramid of number will be upright. In an ecosystem with a small number of primary producers, such as a forest, the pyramid of number will be inverted.
A pyramid of biomass is a graphical representation that shows the biomass of organisms at each trophic level in a food chain. The pyramid of biomass is always upright because biomass is always lost as heat at each trophic level. This means that the biomass of organisms at higher trophic levels is always less than the biomass of organisms at lower trophic levels.