Which of the following is used as biofertilizer?
A. Cyanobacteria
B. Yeast
C. Symbiotic bacteria
D. Free living bacteria

Options

A. A,B,C
B. A,B,D
C. A,C,D
D. A,B,D

Answer

To determine which of the following options is used as a biofertilizer, let's analyze each option step by step:

### Step 1: Understand what biofertilizers are
Biofertilizers are substances that contain living microorganisms, which help in enhancing the fertility of the soil by promoting the growth of plants. They can fix atmospheric nitrogen, solubilize phosphorus, and enhance nutrient availability.

### Step 2: Analyze the options
- **A. Cyanobacteria**: These are photosynthetic bacteria that can fix atmospheric nitrogen into a form usable by plants. They are commonly used as biofertilizers, especially in rice paddies.

- **B. Yeast**: While yeast is used in fermentation and baking, it does not have a significant role in enhancing soil fertility or plant growth. Thus, it is not considered a biofertilizer.

- **C. Symbiotic bacteria**: These bacteria, such as Rhizobium, form symbiotic relationships with legumes and help in nitrogen fixation. They are indeed used as biofertilizers.

- **D. Free living bacteria**: Some free-living bacteria, like Azotobacter, can also fix nitrogen and are used as biofertilizers.

### Step 3: Conclusion
Based on the analysis, both **A. Cyanobacteria** and **C. Symbiotic bacteria** are used as biofertilizers. However, since the question asks for which of the following is used as a biofertilizer, the best answer is **A. Cyanobacteria**.

### Final Answer:
**A. Cyanobacteria**

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