The correct option is A Nutrients
Humus is the organic component of soil, formed by the process of humification of detritus by soil microorganisms.This substance is known as humus. Its specific character is that it is highly resistant to microbial action and so, it undergoes extremely slow decomposition. It is slightly acidic, colloidal and functions as a huge reservoir of nutrients. The carbon dioxide in the atmosphere serves as a reservoir for carbon.