Final answer:
In an auditorium, a large screen on one wall is likely used as a projection surface for presentations, serving a practical rather than decorative or structural purpose(option b).
Step-by-step explanation:
The large screen on one wall of an auditorium with a flat floor is very likely to serve as a projection surface for presentations(option b).
This kind of setup is typical in spaces designed for lectures, films, slideshows, or any event that incorporates visual media. Unlike historical ornamental screens found in castles or temples, which were decorated with artistic scenes, or like the structured proscenium theatre designed for theatrical performances, the large screen in an auditorium serves a modern and practical function. The ambient light in the auditorium can be managed to enhance the visibility of the images projected onto the screen, making it a central feature of any presentation or performance taking place within the space.