There are actually three terms: Ethos, pathos and logos. Each use different methods to capture the attention of your reader and persuade them into doing something by using emotional support or raw facts, depending on what method is used.
The correct answer is free verse (choice C), in which you do not follow any particular rules about rhythm or rhyme. On the other hand, iambic, fixed, and syllable verses follow a certain rhythm, to make the poem look more uniform. Free verse is not restricted in such a way, and allows author to write as the wish.
