Methanogens, a type of archaebacteria, play a role for the human welfare in A. sewage treatment B. biogas productionC. increasing crop productivityD. biocontrol of plant pathogens

Methanogens play a role in sewage treatment plants for degrading the flocs and releasing biogas. In biogas production too they are involved in the formation of biogas from animal wastes in biogas plants. They have no role as biocontrol agents and bio-fertilizers.