Both Ectomycorrhizal Fungi and Rhizobia Are Able to Supply Plants

Both ectomycorrhizal fungi and rhizobia are able to supply plants with usable forms of nitrogen.From what sources do rhizobia and ectomycorrhizal fungi that are associated with plants obtain nitrogen?

A) Fungi absorb N₂ from the atmosphere,and rhizobia obtain nitrogen by decomposition of organic material.
B) Fungi obtain nitrogen by decomposition of organic material,and rhizobia absorb N₂ from the atmosphere.
C) They both absorb ammonia from soil,which they nitrify to NO₂⁻.
D) They both obtain nitrogen by decomposition of organic material.