What are the blocks or platforms used to create levels on a stage called?

The correct choice is "rostra," which refers specifically to the blocks or platforms used to create different levels on a stage. Rostra can be utilized to enhance the visual dynamics of a performance by adding height and depth, allowing for greater staging possibilities and spatial awareness among the actors. This is particularly important in conveying the hierarchy of characters, emphasizing certain actions, and creating an engaging atmosphere for the audience.

Set props, on the other hand, are movable objects on the stage that support the action but do not inherently involve constructing multi-level structures. Set dressing refers to the decorative elements that enhance the visual storytelling of the set but also do not create structural levels like rostra do. Skull cap, in the context of theater, usually refers to a type of overhead structure, often used in sound and lighting design, rather than to platforms for staging.