Domestic sewage mainly contains $A$ wastes which are readily decomposed with the help of $B$. Here $A$ and $B$ refer to:

• A
  $A-$inorganic; $B-$bacteria
• B
  $A-$biodegradable; $B-$decomposers
• C
  $A-$chemical; $B-$microorganisms
• D
  $A-$synthetic; $B-$bacteria