Answer:
Option A, Bacteria
Explanation:
Nitrifying bacteria is a group of aerobic bacteria that converts ammonia in soil into nitrates so that it can be easily taken up by the plants. So basically, in this entire conversion bacteria’s of two distinct group are used – a) bacteria that convert ammonia to nitrites (such as Nitrosomonas, Nitrosospira, Nitrosococcus, and Nitrosolobus ); and b) bacteria that converts nitrites to nitrates
Hence, option A is correct
