Answer:
The factor with the responsibility for nitrogen fixation is bacteria (option C).
Explanation:
The nitrogen that contributes to the formation of proteins comes from plants. Due to the inorganic nature of nitrogen, plants require bacteria to contribute to the assimilation of this element, a process called biological nitrogen fixation.
Nitrogen fixing bacteria in plants are called diazotroph and, in some cases, establish a symbiosis with the plant's roots, the rhizobia.
- The other options, air, animals and lightning, do not correspond to biological nitrogen fixers with the ability to incorporate nitrogen into plants.
