Soybeans Will Have Several Hundred Rhizobium Nodules

Soybeans will have several hundred Rhizobium nodules.A study in Minnesota found that soybeans grown without P₂O₅ fertilizer produced 23.0 bushels per acre,while adding 23 lbs of P₂O₅ per acre gave a yield of 37 bushels per acre.What is the best explanation for this observation?

A) Rhizobium cannot produce PO₄,so you need to add fertilizer that contains P.
B) Rhizobium produces NH₄⁺,so you don't need fertilizer that contains N.
C) Rhizobium produces PO₄ and NH₄⁺,so you don't need any fertilizer.
D) Rhizobium produces PO₄,so you don't need P-containing fertilizer.
E) Rhizobium cannot produce NH₄⁺,so you need to add fertilizer that contains N.