Final answer:
The emphasis on rationalism in the eighteenth and nineteenth centuries brought discipline and structure to the director's role in theater.
Step-by-step explanation:
The emphasis on rationalism in the eighteenth and nineteenth centuries influenced the director's role by bringing discipline and structure. During this period, the Enlightenment and the scientific revolution led to the belief in rational thinking and the application of universal laws. In the realm of theater, this emphasis on reason resulted in directors like Georg II, Duke of Saxe Meiningen, who focused on creating a more cohesive production by paying attention to details such as acting style, costumes, and set design. Therefore, the correct answer is C) Brought discipline and structure.