单选题
The passage mentions that at various points, scientists have believed all of the following to be essential for the nitrogen fixation process EXCEPT
A、
(A) The presence of ammonia
B、
(B) The permeability of cell membranes
C、
(C) The presence of rhizobia
D、
(D) The synthesis of amino acids
E、
(E) Nitrogen-containing molecules like nucleotides
【正确答案】
E
【答案解析】
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