What is a key feature of architectural CMUs?

Architectural Concrete Masonry Units (CMUs) are specifically designed with a focus on aesthetic appeal, which distinguishes them from standard CMUs that are primarily utility-driven. This emphasis on design means that architectural CMUs often come in a variety of textures, colors, and finishes, making them suitable for visible architectural elements in buildings. Their visual characteristics can enhance the overall look of a structure, making them a popular choice for both interior and exterior applications where appearance is a significant consideration.

The other options do not accurately represent the defining features of architectural CMUs, as their weight can vary, they are not limited to exterior use, and while some may incorporate recycled materials, it's not a universal requirement for all architectural CMUs. This focus on design and aesthetics is what sets architectural CMUs apart in masonry work, making choice B the most accurate descriptor of their key feature.