Plants Require Nitrogen for Life, but Only Certain Forms of Soil

Plants require nitrogen for life, but only certain forms of soil nitrogen are accessible to most plants.Which forms are directly useful to plants, and from where do these come?

A) NH₄⁺ and NO₃^- from ammonification to form ammonium cations and nitrification to form nitrate anions
B) N₂ and organic nitrogen (nitrogen bound to carbon-based molecules) from denitrification to form molecular nitrogen and biosynthesis to form organic nitrogen
C) NO₂^- from nitrification to form nitrite anions