Answer:
I think it's option A
Explanation:
Nitrogen fixing bacteria such as rhizobium, which lives in the root nodules of leguminous plants, help convert inert nitrogen to ammonia. Once the nitrogen has been fixed in the soil, the plants can absorb nitrogenous compounds through their roots. The process of absorption is known as assimilation.
Besides, nitrogen can only be fixed in two ways; atmospheric fixation (involving lightening) and industrial fixation (manufacturing ammonia under high temperature and pressure). I hope this helps