Kanika noticed that her potted plant was not growing healthily. She put few earthworms into the pot. After a few weeks, she noticed that her plants looked healthier. What could be the possible reason for this?

• A. The earthworms ate up the pests in the soil.                         
• B.        The earthworms helped the plant to take in water.                    
• C.        The earthworms allowed the plant to make food faster.                
• D.        The earthworms increased the air and nutrient content of the soil.