You didn't provide us with the text.
Twain accomplishes his purpose chiefly through telling a story within a story, also called a "frame story".
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.
Answer:
similes
Explanation:
Because they are introduced by "as" and "like"
