The Specific Relationship Between a Legume and Its Mutualistic Rhizobium

The specific relationship between a legume and its mutualistic Rhizobium strain probably depends on

A) each legume having a chemical dialogue with a fungus.
B) each Rhizobium strain having a form of nitrogenase that works only in the appropriate legume host.
C) each legume being found where the soil has only the Rhizobium specific to that legume.
D) specific recognition between the chemical signals and signal receptors of the Rhizobium strain and legume species.
E) destruction of all incompatible Rhizobium strains by enzymes secreted from the legume's roots.