Why Is Nitrogen Fixation an Essential Process

Why is nitrogen fixation an essential process?

A) Fixed nitrogen is often the limiting factor in plant growth.
B) Nitrogen fixation can only be done by certain prokaryotes.
C) Nitrogen- fixing capacity can be genetically engineered.
D) Nitrogen fixation is very expensive in terms of metabolic energy.
E) Nitrogen fixers are sometimes symbiotic with legumes.