What may also supply one set of service-entrance conductors?

One set of service-entrance conductors can be supplied by various means, which is why the correct answer encompasses all the provided choices.

Service-entrance conductors are the wires that bring electrical power from the utility supply to the building's electrical system. This can be achieved through underground feeders, which involve cables buried underground to protect them from environmental factors and enhance safety. Overhead lines are another common method, where power is delivered through aerial conductors mounted on utility poles.

In addition, transformer installations can also supply service-entrance conductors. If a transformer is used, it steps down the high voltage from the utility supply to a usable level, allowing for the connection of service-entrance conductors to the lower voltage distribution network.

Understanding that service can come from any of these options reflects a comprehensive grasp of electrical supply methods as per the National Electrical Code (NEC) and illustrates the versatility of electrical installations, particularly in varying environmental contexts.