Final answer:
A parapet is an extension of a wall past the roof of a building, mainly used to conceal roof equipment and provide a finished look.
Step-by-step explanation:
A parapet is the extension of a wall past the top of the roof. Parapets are used to hide unsightly roof equipment and HVAC units, providing a building with a finished and more aesthetically pleasing appearance. Despite having a practical function in hiding roof equipment, parapets can also add an architectural ornament to the building façade. In the context of a multiple-choice question, the correct answer to fill in the blank would be 'a) Parapet walls'. They can be part of the architectural design of a range of building styles and may include additional design features such as arcades, pilasters, and decorative pediments.