ANS:B - 2.0

The ratio of maximum daily sewage flow to the average daily sewage flow in sewer mains can vary depending on factors such as population density, water usage patterns, and hydraulic design criteria. However, a common assumption for sewer mains with diameters ranging from 0.5 to 1 meter is a ratio of 2.0. This means that the maximum daily sewage flow is assumed to be twice the average daily sewage flow. This assumption helps engineers design sewer mains to accommodate peak flow conditions while ensuring that the system can effectively convey wastewater under normal operating conditions. So, the correct option is: 2.0.