Organisms use nitrogen in which one of the following ways?
A)Certain bacteria living in the roots of plants convert nitrogen to a form plants
can use, and animals obtain their nitrogen by eating those plants.

B)Plants absorb nitrogen from the air in photosynthesis and add it to the sugars
they produce

C)Certain bacteria convert nitrogen to a form animals can use, Wd animals obtain
their nitrogen by inhaling this nitrogen.

D)Animals absorb nitrogen from the air they breathe and incorporate it into their
tissues

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

d. planting trees

the trees take in carbon to make oxygen.