What type of sculpture relies on three-dimensional projection from a flat surface?

The correct answer is bas-relief, which refers to a sculptural technique where the figures are carved into a flat surface, projecting out from it while still remaining attached. This style creates a sense of depth and dimension without fully separating the figures from the background. Bas-relief is characterized by a shallow depth of projection, making it easier to incorporate into architectural elements or as part of decorative panels.

Haut relief, on the other hand, involves a greater degree of projection than bas-relief, and typically the figures are more prominent and may almost be free-standing. Frottage is a technique related to texture made by rubbing, and it does not involve sculpting from a flat surface in a traditional sense. Monotype refers to a printmaking process that produces a single, unique print rather than a sculptural form. Thus, bas-relief stands out as the correct choice for a type of sculpture that relies on three-dimensional projection from a flat surface.