Trophic levels are formed by

Options

A. Organisms linked in food chain
B. Only plants
C. Only animals
D. Only carnivores

Explanation

### Step-by-Step Solution:

1. **Understanding Trophic Levels**: Trophic levels refer to the different levels in a food chain or food web where organisms are categorized based on their feeding relationships.

2. **Identifying the Components**: In an ecosystem, there are primarily three types of organisms that form these levels:
- **Producers**: These are typically plants or autotrophs that produce energy through photosynthesis.
- **Primary Consumers**: These are herbivores that consume the producers.
- **Secondary Consumers**: These are carnivores that eat the primary consumers.

3. **Linking Organisms in a Food Chain**: The organisms at each trophic level are linked through feeding relationships. For example, plants (producers) are consumed by herbivores (primary consumers), which are then consumed by carnivores (secondary consumers).

4. **Defining Trophic Levels**:
- **Trophic Level 1**: Producers (e.g., plants)
- **Trophic Level 2**: Primary consumers (e.g., herbivores)
- **Trophic Level 3**: Secondary consumers (e.g., carnivores)

5. **Conclusion**: Therefore, trophic levels are formed by organisms that are linked in a food chain, which includes producers, primary consumers, and secondary consumers.

### Final Answer:
Trophic levels are formed by organisms linked in a food chain.

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