11. During the symbiotic nitrogen fixation between legumes and Rhizobium, the nitrogenase in the bacteria is highly sensitive to oxygen. How does the plant help resolve this issue?
(A) The plant closes its root stomata to prevent soil oxygen from entering.
(B) The plant synthesizes leghemoglobin, which binds oxygen in the microenvironment to maintain a low-oxygen state.
(C) The plant converts oxygen into salicylic acid to provide as a carbon source for the bacteria.
(D) Rhizobium itself secretes a thick Casparian strip to completely isolate oxygen.