Fill blank (ii).

Directions: Read the following passage having some numbered blanks.

Biogas ______(i)_____ obtained from animal dung and other agricultural wastes.  Animal dung and other agricultural wastes are mixed with water and ________(ii)_______ into a digester. In the absence of air, the biomass ________(iii)_______ to give a combustible gas, _________(iv)_______ is a mixture of gases like methane, carbon dioxide, hydrogen and hydrogen sulphide.