Answer:
The correct option is C
Step-by-step explanation:
Anaerobic bacteria used in sewage treatment helps to reduce the volume/amount of sludge in the sewage thereby producing methane gas from it. Some companies produce there own (not for sale) methane gas (as an alternate source of energy) through this process. Thus, a decrease in the amount of this bacteria (perhaps through death as described in the question) will lead to a decreased production of methane gas.