A. A discussion of what happened leads to the revelation that Cesario is Viola.
The correct option is A. The sword fight between Sebastian, Sir Andrew, and Sir Toby is a key moment in the play that develops the plot in several ways. After the fight, Sebastian is confused about what happened and is confronted by Viola, who he believes to be Cesario. Viola reveals her true identity to Sebastian, and he is amazed to discover that his sister is alive and well. This revelation leads to the resolution of the play's central love triangle, as Viola is finally able to reveal her love for Orsino.