Answer: C) nitrogen fixation
Step-by-step explanation:
Nitrogen fixation is the process by which atmospheric nitrogen is fixed in the soil by the soil bacteria. The nitrogen is present in the atmosphere but cannot be used by the plants directly in the inorganic form thus the soil bacteria convert the atmospheric nitrogen into other forms such as nitrates and ammonia. The plants absorb these forms through their roots and in return the bacteria receives the nourishment. The nitrogen is essential for the growth of the crops in the sense it is an important ingredient of aminoacids which is required for the production of proteins, and nucleic acids.