Respuesta :
D is correct; Mark Antony opposed Brutus and Brutus was for the republic. A is incorrect because they did cause problems for each other. B is incorrect because Cassius is not the antagonist and Mark was not the protagonist. Finally, C is incorrect because Mark did not play a minor role in the play.
The answer is D. I guess in some peoples eyes Brutus is the protagonist except during Caesar's rule when the tables are turned. After this point Antony is setup to become the protagonist.