Use of Synthetic Fertilizers Often Leads to the Contamination of Groundwater

Use of synthetic fertilizers often leads to the contamination of groundwater with nitrates. Nitrate pollution is also a suspected cause of anoxic "dead zones" in the ocean. Which of the following processes is most likely to help reduce nitrate pollution?

A) adding methanogens to the soil
B) adding nitrifying bacteria to the soil
C) adding denitrifying bacteria to the soil
D) using ammonia instead of nitrate as a fertilizer