What defines a solid beam?

A solid beam is typically defined by its structural design and cross-sectional shape. The option indicating a simple rectangular cross section refers specifically to the common shape and uniformity that characterizes many solid beams, particularly in construction and engineering.

In this context, a simple rectangular cross section means that the beam has a consistent width and height throughout its length, which provides uniform strength and stability. This design allows solid beams to effectively carry loads and resist bending or shear forces, making them a fundamental component in various structures such as bridges, buildings, and frameworks.

Other design features or mechanisms mentioned in the other choices may be relevant to specific types of beams or structural components, such as trusses or sliding structures, but they do not accurately define what a solid beam is in its most basic and widely recognized form.