What do audience members see of the stage from their seating position?

The correct answer is sight lines, as this term refers to the visual lines of sight that audience members have to different parts of the stage from their seating positions. Sight lines are critical in theatre as they determine what the audience can see, which influences how the performance is received. Good sight lines ensure that all audience members can view the action on stage without obstructions, allowing for a more engaging and immersive experience.

The other choices offer different aspects of staging. The acting area refers to the physical space where performances take place, but it doesn't specifically address how visible that area is from various seating positions. Set dressing pertains to the decoration and arrangement of the stage to create a specific environment or context for the performance but does not directly relate to audience visibility. Rostra refers to raised platforms used in staging, which can enhance performance dynamics but again doesn't directly imply the visibility aspect for the audience. Thus, sight lines distinctly encapsulate the concept of visibility from the audience's perspective.