Answer: B. all the nitrogen obtained by animals come from plants.
Step-by-step explanation:
Animals are unable to use inorganic bacteria until plants absorb it and then animals get it from the plants so in effect, all the nitrogen obtained by animals comes from plants.
Plants absorb nitrogen in the form of Nitrates which were fixed by bacteria from Nitrites which were further fixed from Ammonium which was fixed from atmospheric Nitrogen all by bacteria.