Unreinforced Masonry buildings are easily recognized by which of the following characteristics?

Unreinforced masonry buildings are primarily characterized by their structural composition, and the presence of king rows of brick is a defining feature. King rows, or courses of headers, are horizontal rows of bricks that often appear in the construction of such buildings, providing a distinct appearance associated with masonry work. They demonstrate a traditional style of construction where bricks are laid without the internal reinforcement that could enhance structural integrity.

In contrast, flat rooflines can be found in various types of buildings, not just unreinforced masonry, as they are typically a design choice rather than a structural characteristic. Metal frames are indicative of a different type of construction, typically seen in modern buildings that require lightweight structures, which would not align with the unreinforced masonry style. Vinyl siding is an exterior finishing material commonly used in contemporary constructions that do not relate directly to the characteristics of unreinforced masonry.

Thus, king rows of brick stand out as a hallmark feature of unreinforced masonry buildings, highlighting the traditional methods of construction and the specific materials used in their formation.