Answer is option A.
When organisms eat other organisms, energy is transferred from one organisms to other. According to 10% law of energy transfer, only 10% of the available energy gets transferred to next trophic level of organisms. In this question apex or top consumer have 500 to 1000 kilograms of biomass. To have 500 to 1000 kilograms of biomass at apex level, the producers in food chain must have much lager biomass than 1000 kilograms to support biomass of 500 to 1000 kilograms at apex consumers. It is because most of the energy is lost as heat during transfer of energy from one trophic level to another.