A single ladder is virtually identical to what type of ladder?

A single ladder, which is typically a straight and non-adjustable structure, is virtually identical to the base section of an extension ladder. The base section of an extension ladder also retains a similar straight design, providing support for the entire structure when extended. Both types of ladders require proper placement against a solid, stable surface to ensure safety during use.

In contrast, a step ladder has a widened base with a triangular frame and folds for storage, which differs fundamentally from the single ladder's design. Multi-purpose ladders are versatile and can be configured in various ways, including as a step ladder or extension ladder, but they are not directly comparable to a single ladder in function at a basic level. A platform ladder features a flat platform at the top for work, which alters its use and design from that of a single ladder. Thus, identifying a single ladder's closest resemblance within these options leads us to the base section of an extension ladder.