Choose the correct answer from the list below. Not all of the answers will be used.
-_______________ is the original nitrogen source for the nitrogen found in amino acids.

A)atmospheric nitrogen (N₂)
B)3-phosphoglycerate
C)cumulative
D)nitrogen fixation
E)B₁₂
F)histidine
G)tetrahydrofolate
H)committed
I)pyridoxal phosphate
J)enzyme multiplicity
K)MoFe cofactor
L)ammonia (NH₃)