I would say that the principle means of characterization employed by the author is dialogue. Since Romeo and Juliet is a play, everything we know actually comes from the conversations, be it a dialogue, or a monologue.
I believe the correct answer is hyperbole.
Hyperbole is a rhetorical figure of speech which show some kind of exaggeration - in this particular example, the hyperbole is found in the words 'an hundred years.' This is so because the poet won't really spend a hundred years to praise the woman's eyes, but is rather exaggerating a bit.
19 Sentence 20 is a fragment
