Which is a Primary Symbiotic Nitrogen Fixer

Question

Which is a primary symbiotic nitrogen fixer
A)Azotobacter
B)Rhizobium
C)Cyanobacteria
D)Clostridium

Accepted Answer

Rhizobium is a primary symbiotic nitrogen fixer, forming a symbiotic relationship with leguminous plants to convert atmospheric nitrogen into a form that the plant can use.