Instead of checking definitions one by one, first ask what the word "buzzing" is doing: is it comparing, replacing, imitating, or contradicting something?
It is not comparing two things with "like" or "as" (so not simile), it is not swapping in a related object for bees (so not metonymy), and there is no self-contradicting idea to call it a paradox. What "buzzing" does is copy the real sound made by bees, the same way "hiss," "click," and "moo" copy the sounds snakes, cameras, and cows make.
Words built to sound like what they describe are called onomatopoeia, so the answer is C.