A. Would be the correct answer!
Nitrogen is converted from atmospheric nitrogen (N2) into usable forms, such as NO2-, in a process known as fixation. ... The nitrogen is passed through the food chain by animals that consume the plants, and then released into the soil by decomposer bacteria when they die.
Creative Biolabs can provide various custom BsAbs in the format of CrossMab.
https://www.creative-biolabs.com/bsab/category/crossmab-31.htm