ANS:D - all (a), (b) and (c)

Bio-fertilisers are indeed beneficial for improving various aspects of soil quality. They enhance the nutrient supply, texture, and water holding capacity of the soil. So, the correct option is: all (a), (b), and (c). Explanation:

1. Nutrient Supply: Bio-fertilisers contain beneficial microorganisms such as nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and mycorrhizal fungi. These microorganisms help in increasing the availability of essential nutrients like nitrogen, phosphorus, and potassium to plants by fixing atmospheric nitrogen and solubilizing insoluble forms of nutrients in the soil.
2. Texture Improvement: The presence of organic matter in bio-fertilisers improves soil structure and texture. It encourages the formation of soil aggregates, which enhances soil porosity, aeration, and water infiltration. This leads to better root penetration and overall soil health.
3. Water Holding Capacity: Bio-fertilisers contribute to the improvement of soil water holding capacity. Organic matter in bio-fertilisers acts as a sponge, holding moisture in the soil and making it available to plants for a longer duration. This helps in reducing water stress during dry periods and improving plant growth.
4. Environmental Benefits: Additionally, bio-fertilisers are renewable and environmentally friendly alternatives to chemical fertilisers. They do not contain harmful synthetic chemicals and do not contribute to soil and water pollution, making them sustainable options for agriculture.