Answer: first.
- A first
- B second
- C third
- D fourth
Correct answer: A. first
Explanation: Producers form the first trophic level of a food chain.
Energy pyramid showing a simple food chain (producer to herbivore to carnivore) with energy decreasing roughly tenfold at each trophic level.
Concept context
Ecosystems, food chains, energy flow, nutrient cycles, biodiversity, and conservation.