Final answer:
The correct answer to the architectural feature question is a wing, which is part of a building that projects from and is subordinate to the main structure.
Step-by-step explanation:
The architectural feature that is described as a part of a building projecting from and subordinate to a central or main part is most accurately defined as a wing. An annex typically refers to a separate building or structure that has been added to a larger one, while a turret is a small tower that projects vertically from the wall of a building. A foyer, on the other hand, is an entrance hall or other open area in a building used by the public, especially a hotel or theater. In the context of the detailed description provided, a wing would be the part of the building that extends from the main structure, but remains subordinate to it.
The role of such features can be seen in historical architectural styles, such as the neo-Gothic example mentioned. Here, the buttresses would not technically be considered a wing, but they are relevant as an archetypal example of substructures that project from the main structure and are crucial to the support and integrity of the building, much like a wing supports the overall plan of a building.