Which of the following statements is/are correct ?

Options

A. In paddy fields, cyanobacteria serve as an important biofertiliser.
B. Vermicompost consists of organic matter prepared by the action of earthworms on human or animal waste.
C. The important examples of cyanobacteria as biofertilisers are Anabaena, Nostoc and Oscillatoria.
D. All of these

Answer

To determine which statements are correct regarding the role of microbes in human welfare, particularly focusing on cyanobacteria and vermicomposting, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Analyzing Statement A**:
- **Statement**: "In paddy fields, cyanobacteria serve as an important biofertilizer."
- **Explanation**: This statement is correct. Cyanobacteria, such as Anabaena, play a significant role in nitrogen fixation in paddy fields. They form a symbiotic relationship with aquatic ferns like Azolla, which enhances nitrogen availability and increases rice yield.

2. **Analyzing Statement B**:
- **Statement**: "Vermicompost consists of organic matter prepared by the action of earthworms on human or animal waste."
- **Explanation**: This statement is also correct. Vermicomposting involves the breakdown of organic matter by earthworms, resulting in nutrient-rich compost that is beneficial for soil and plant growth. It is known for improving soil structure and fertility.

3. **Analyzing Statement C**:
- **Statement**: "The important examples of cyanobacteria as biofertilizers are Anabaena, Nostoc, and Oscillatoria."
- **Explanation**: This statement is correct as well. Anabaena, Nostoc, and Oscillatoria are all examples of cyanobacteria that are used as biofertilizers due to their ability to fix atmospheric nitrogen, making it available for plant use.

4. **Conclusion**:
- Since all three statements (A, B, and C) are correct, the final answer is option D: "All of these."

### Final Answer:
**D: All of these statements are correct.**