Conversion of organic nitrogen into ammonia, `N_(2)` gas into ammonia, nitrates into ammonia and ammonia into nitrates are respectively known as
A. nitrogen-fixation, nitrate reduction, nitrification, ammonification
B. ammonification, nitrogen-fixation, nitrate reduction, nitrification
C. nitrification, ammonification, nitrogen-fixation, nitrate reduction
D. nitrogen-fixation, nitrate reduction, denitrification, ammonification