Nitrogen Fixation Is a Difficult Process Because ________

Nitrogen fixation is a difficult process because ________.

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