Identify the odd one out in the context of biogas composition.

Which of the following is mainly produced by the activity of anaerobic bacteria on sewage?

What is the group of bacteria responsible for the production of biogas called?

Consider the following statements about methanogenic bacteria:
$I.$ Methanogenic bacteria are commonly found in the anaerobic sludge formed during sewage treatment.
$II.$ These bacteria also occur in the rumen of cattle,where they act upon cellulosic material to break down cellulose.
$III.$ They play a very important role in the nutrition of cattle by digesting cellulosic material.
Which of the statements given above are correct?

Pollution from animal excreta and organic waste from the kitchen can be most profitably minimized by

Assertion $A$: Herbivores release methane gas into the atmosphere.
Reason $R$: Herbivores consume a cellulose-rich diet.
Which option is correct for Assertion $A$ and Reason $R$?