Pick the odd one out with respect to primary producers.
Hydrilla, Vallisneria, Spirogyara, Insects.

Explanation

To solve the question of picking the odd one out with respect to primary producers from the options given (Hydrilla, Vallisneria, Spirogyra, Insects), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Categories**:
- Look at the four options: Hydrilla, Vallisneria, Spirogyra, and Insects.
- Hydrilla, Vallisneria, and Spirogyra are all types of plants, specifically freshwater aquatic plants.

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