Which piping connects the source to the risers or branches, or both?

The correct choice identifies "Main Lines" as the piping that connects the source of the medical gas system to either risers or branches. Main lines serve as the primary pathway for medical gases to travel from the central source, which could be an oxygen tank, manifold, or other supply systems, directly to the locations where the gases are needed in a healthcare facility.

Main lines are designed to handle the volume and pressure required for effective gas distribution, ensuring that adequate supply reaches various areas, including patient rooms and treatment areas. This infrastructure is vital for the overall efficiency and reliability of the medical gas system.

In contrast, other types of piping serve different functions. Service lines typically refer to the smaller conduits that distribute gases from the main lines to the points of use but do not connect directly to the source. Supply lines may refer more generally to any pipe supplying gas, but it is the main lines that specifically connect the source to the larger distribution network. Distribution lines are responsible for carrying gases within a localized area but do not connect to the main source directly. Thus, the designation of this piping role is crucial for understanding the layout and function of medical gas systems.