The given diagram shows nitrogen cycle in the ecosystem. P, Q, R, S and T represent different chemical conversion steps in the cycle.
Which process (P - T) is correctly paired with the organismal group performing that step?
I. P Nitrobacter
II. Q Bacteria symbiotic with plants
III. R Denitrifying bacteria
IV. S Nitrifying bacteria
V. T Nitrogen fixing bacteria, such as Rhizobium or cyanobacteria
AIII, IV and V
BIV and V
CI, III and IV
DIII and IV