Which document issued by the Architect illustrates what is to be built?

The correct answer is "Plans" because this term specifically refers to technical drawings or diagrams that detail the specifications for a construction project, including dimensions, materials, and other important information required for construction. Plans provide a clear and organized way to understand how a building or structure should be constructed, making them essential for contractors and builders when executing the project.

While blueprints can often be used interchangeably with plans, they are traditionally a specific type of reproduction of architectural drawings. The term "plans" is broader and encompasses all necessary drawings used in construction, which can include blueprints as well as other forms of documentation.

Architectural renderings, on the other hand, primarily serve the purpose of visualizing the project's appearance, focusing on aesthetic aspects rather than detailed construction requirements. A design report is typically a written document that summarizes the project goals, requirements, and design studies, but it doesn't directly illustrate what is to be built in the same way that plans do. Thus, "Plans" is the most accurate choice for the document that illustrates what is to be built.