Correct option is C
The correct option to fill in the blank is (c) Monotonous.
Explanation: "Monotonous" means dull and repetitive, which makes sense for an unchanging and annoying musical rhythm.
Meanings of other options:
· Irreverent: Showing a lack of respect, inappropriate for this context.
· Recusant: Someone who refuses to submit to authority, irrelevant here.
· Coherent: Logical and consistent, but doesn't fit the context of annoyance.