What type of electrical system would commonly be found in homes constructed before 1950?

Homes constructed before 1950 commonly utilized BX systems, which refer to armored cable, also known as flexible metal conduit cable. BX cable consists of insulated conductors encased in a flexible, metallic sheath that provides some protection against physical damage and electromagnetic interference. This type of wiring was popular due to its durability and the inherent grounding capability offered by the metal armoring.

In contrast, the other options represent wiring methods that became more prevalent after the mid-20th century. Conduit, while still in use today, typically involves rigid and/or flexible tubes that enclose electrical wires and is more commonly used in commercial or industrial settings. Greenfield, or flexible metallic conduit, is similar to BX but lacks the additional insulation that BX offers, making it less common in residential applications prior to 1950. Romex, or NM (non-metallic) cable, represents a modern wiring method that started being widely used in homes after the introduction of the National Electrical Code revisions post-1950. Therefore, BX is the appropriate choice for homes built before that time.