The correct answer is A. upright.
A pyramid of biomass is a graphical representation of the biomass of organisms at each trophic level in a food chain. The biomass of an organism is its mass of living material. The pyramid of biomass is upright in grassland ecosystems because the biomass of producers is greater than the biomass of consumers. This is because producers, such as plants, are able to convert sunlight into energy through photosynthesis. Consumers, such as herbivores and carnivores, cannot do this and must rely on producers for their energy. As a result, there is more biomass in the producer trophic level than in the consumer trophic levels.
An inverted pyramid of biomass is a graphical representation of the biomass of organisms at each trophic level in a food chain where the biomass of consumers is greater than the biomass of producers. This can occur in ecosystems where the consumers are very efficient at converting the energy they consume into biomass, or where the producers are very inefficient at converting sunlight into energy.
A spindle-shaped pyramid of biomass is a graphical representation of the biomass of organisms at each trophic level in a food chain where the biomass of producers and consumers is similar. This can occur in ecosystems where the producers and consumers are both efficient at converting energy into biomass.
None of these is the correct answer because it does not describe the shape of the pyramid of biomass in grassland ecosystems.