Study the following flow chart of biogas production and select the correct option for $A, B$ and $C$.
Stage $III$: $C$
Stage $II$: Organic acids $\xrightarrow{B}$ $C$
Stage $I$: Soluble compounds or monomers $\xrightarrow{A}$ Organic acids
(Note: The flow chart shows: Proteins,Fats,Cellulose,Hemicellulose $\rightarrow$ Soluble compounds or monomers $\xrightarrow{A}$ Organic acids $\xrightarrow{B}$ $C$)

• A
  $A-$Methanogenic bacteria,$B-$Fermentative microbes,$C-CO_{2}$ and hydrogen (biogas)
• B
  $A-$Anaerobic microorganisms,$B-$Methanococcus,$C-CO_{2}$ and nitrogen (biogas)
• C
  $A-$Fermentative microbes,$B-$Methanogenic bacteria,$C-CO_{2}$ and methane (biogas)
• D
  $A-$Aerobic microorganisms,$B-$Methanobacter,$C-CO_{2}$ and methane (biogas)