Complete the following cycle given as Fig.2.4 by filling the blanks (a), (b), (c), (d).

a) Lightning fixes atmospheric nitrogen.

b) Nitrogen-fixing bacteria and blue-green algae fix atmospheric nitrogen.

c) Nitrogenous waste from excretion by animals and plants and decomposition of dead plants and animals.

d) Nitrogen released by bacteria from nitrogenous compounds present in soil into air.