Which Statement Correctly Describes the Role of Nitrogen Fixation in the Nutrient

Which statement correctly describes the role of nitrogen fixation in the nutrient cycle?

A) N₂ is taken in by green plants and transformed into nitrogen-rich protein.
B) N₂ is inhaled by herbivores and transformed into ammonia, which can be dissolved in their blood.
C) NH₄⁺ is converted by certain bacteria into complex proteins that can then be ingested by animals.
D) N₂ is taken up by certain bacteria that can change it into chemically available forms usable by plants.