The answer is; A
Denitrification is carried out by denitrifying bacteria such as Paracoccus denitrificans and Thiobacillus denitrificans. These bacteria hydrolyze nitrates and nitrites into molecule nitrogen and are significant in the Nitrogen Cycle. The complete process of denitrification can be shown in a single redox equation below;
2 NO3− + 10 e− + 12 H+ → N2 + 6 H2O