43. Why is nitrogen fixation needed for the growth of some plants?
(A) Nitrogen fixers are sometimes symbiotic with legumes.
(B) Nitrogen fixation can only be done by certain prokaryotes.
(C) Nitrogen fixation can produce metabolic energy for plants’ growth.
(D) Fixed nitrogen is a limiting factor for plant growth.
(E) Nitrogen-fixing capacity is varied in many different plants.
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