Work planes are utilized to establish which type of planes?

Work planes serve as foundational references in engineering design, specifically designed for creating and manipulating two-dimensional sketches. These planes are critical during the initial phases of the design process, as they provide a flat, defined surface on which engineers can accurately draft geometric shapes, outlines, and other design elements.

By establishing a work plane, designers can ensure that all components of the design are aligned and proportionate, which is essential for the later stages of modeling and constructing three-dimensional objects. This emphasis on a two-dimensional base is particularly important in Computer-Aided Design (CAD) programs, where sketches need to be created before turning them into 3D models.

In contrast, options regarding curved planes, surface treatment planes, and solid planes involve more specialized aspects of engineering and do not directly relate to the foundational work that occurs on a two-dimensional plane in the early stages of design development. Thus, the specification of two-dimensional sketch planes as the correct answer highlights their fundamental role in the engineering design process.