Which of the following wiring methods is permitted by the NEC® for the service-entrance conductors for residences?

The correct answer is that rigid polyvinyl chloride conduit (PVC) is a permitted wiring method for service-entrance conductors for residences according to the National Electrical Code (NEC). PVC conduit is highly favored in residential applications because it is lightweight, resistant to corrosion, and relatively easy to install.

The NEC allows PVC conduit to be used for service-entrance conductors due to its ability to provide adequate protection against physical damage and its durability in various environmental conditions. Additionally, PVC is non-conductive, offering an additional layer of safety concerning electrical conduction.

When considering other wiring methods, they have different applications and restrictions in the NEC. Rigid metal conduit, for example, is allowed but has more stringent requirements regarding grounding and bonding. Flexible metal conduit, while useful in specific scenarios, is typically not recommended for service entrances due to its limited protection against physical damage. Non-metallic sheathed cable is used in many residential applications but is not designed for outdoor use and thus wouldn’t provide the necessary protection for service-entrance conductors exposed to the elements.

Hence, PVC's attributes make it the most suitable option in this context for safely handling service-entrance conductors in residential wiring.