He made that poor piano moan with melody.
o blues!
swaying to and fro on his rickety stool
he played that sad raggy tune like a musical fool.
sweet blues!
coming from a black man's soul.
o blues!

the phrases “o blues! ” and “sweet blues! ” are examples of
alliteration.
repetition.
hyperbole.
simile.

B) Repetition.

Explanation: Repetition is a literary device that consists in repeating a word or phrase in a text to emphasize on an idea or a meaning. It is often used as a rhetorical device to add more power to certain words or sentences. In the given lines, we can see a clear example of repetition, in the phrases "O Blues", "Sweet Blues" and then again "O Blues" which helps to emphasize in this phrases and also create rhythm in the text.

a omg *hides wit stranger*