Which of the Following Is Not True Regarding Ammonia and Fertilizers

Which of the following is not true regarding ammonia and fertilizers?

A) Ammonia gas is seldom an effective plant fertilizer, since it is usually consumed by the bacteria in the soil.
B) Many fertilizers are made from ammonia synthesized by the Haber process
C) Researchers are looking for ways to incorporate the genes for nitrogenase into crop plants so that not as much fertilizer is needed
D) Both ammonium and nitrate ions are frequently used in fertilizers