The right answer is: pathos.
Ethos, pathos and logos are rhetorical devices. They are appeals that intend to persuade the audience of something. In the excerpt we're analyzing here, Brutus is using pathos, which is an appeal to the audience's emotions. Pathos may be used to inspire pity, or anger, for instance. The speaker's goal is to make the audience feel something of his choice in order to achieve some other purpose. Brutus seems to be intentionally offending - or claiming to have offended - a specific group of people: the ones who are rude and vile, the ones who are not Romans.
Ethos is appeal to ethics, logos is an appeal to logic, and cosmos is not a rhetorical device.
