Rhizobium is an example of:

Options

A. Biofertilizer
B. Biopesticide
C. Biopesticide
D. Symbiotic fungus

Explanation

To determine what Rhizobium is an example of, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Rhizobium**: Rhizobium is a type of bacteria that is known for its role in nitrogen fixation.

2. **Understand Nitrogen Fixation**: Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related compounds in soil, making it available for plant uptake.

3. **Symbiotic Relationship**: Rhizobium forms a symbiotic relationship with leguminous plants (such as peas and beans). In this relationship, the bacteria live in the root nodules of the plants and provide them with fixed nitrogen.

4. **Bio-Fertilizer Definition**: A bio-fertilizer is a substance that contains living microorganisms, which, when applied to seeds, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promote growth by increasing the supply or availability of primary nutrients to the host plant.

5. **Conclusion**: Since Rhizobium is a nitrogen-fixing bacterium that enhances the nutrient content of the soil through its symbiotic relationship with legumes, it qualifies as a bio-fertilizer.

### Final Answer:
Rhizobium is an example of a **bio-fertilizer**.

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