Nitrogen Fixation Is a Difficult Process Because

Nitrogen fixation is a difficult process because .

A) there is so little nitrogen in the atmosphere
B) of the high polarity of nitrogen molecules preventing them from dissolving in biological fluids, such as those inside cells
C) nitrogen exists in the atmosphere primarily as its oxides which are very unreactive
D) of the extreme toxicity of nitrogen
E) nitrogen is very unreactive, largely due to its triple bond