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

Options

A. each legume having a specific set of early nodulin genes.
B. each Rhizobium strain having a form of nitrogenase that only works 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 & signal receptors of the Rhizobium strain and legume species.

Answer

D