The correct option is B trophic level
Biomass is the mass of living material at each trophic level like the biomass of plants in a rainforest or the biomass of earthworms in the soil. Biomass not only gives an idea of the mass but also of the sample size at each trophic level. Biomass is the mass of living material in each organism multiplied by the total number of organisms in that trophic level. So, you also know how many organisms are actually present.