Sewer pipes need be checked for

ANS:C - both (a) and (b)

Sewer pipes typically need to be checked for both minimum flow and maximum flow. Minimum flow ensures that there is sufficient flow to prevent issues such as sediment buildup and blockages, while maximum flow ensures that the pipes can handle peak wastewater flow without overflowing or causing backups. So, the correct answer is "both (a) and (b)."