This comes from "Life is a Dream", by Pedro Calderón de la Barca.
The correct answer to the conflict Astolfo is alluding to is option d. Without a named successor, there would be a civil war.
In order to avoid conflict, even though Astolfo is in love with Rosaura, he will marry Estrella in order to inherit the throne and by King Basilio's successor.
Answer
d. Without a named successor, there could be a civil war.
Explanation: