sentence2_structure: Pyramid ecosystem<>is used<>to show energy flow through the trophic levels$$$Pyramid ecosystem<>to show<>energy flow
sentence1: Pyramid ecosystem modeling can also be used to show energy flow through the trophic levels; pyramids of energy are always upright since energy decreases at each trophic level.
sentence2: Pyramid ecosystem is used to show energy flow through the trophic levels.
question: What is used to show energy flow through the trophic levels?