Final answer:
The correct answer is option a. 20th century.
Step-by-step explanation:
The fourth wall is often broken in the world of theater. The fourth wall refers to the imaginary wall that separates the actors on stage from the audience. When the fourth wall is broken, the actors directly address the audience, breaking the illusion of separation between the stage and the real world. This technique allows for a more interactive and engaging experience for the audience.
Breaking the fourth wall has been used in theater for centuries, but it became more common in the 20th century and continues to be used in the 21st century. It is often employed for comedic effect, to create a sense of intimacy between the actors and the audience, or to challenge and subvert traditional theatrical conventions.