In some ponds, ducks are bred to increase the growth of carps. Why?

1) Litter of ducks promotes the growth of algae.
2) Algae are food for invertebrates.
3) Carps feed on invertebrates.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.