The correct option is B A euphemism
Option C: A 'euphemism' is a substitute for a term that sounds harsh or blunt. For example, instead of bluntly telling someone that his/her work isn't good, one can tell him/her that the work can be better. In the given sentence, the word 'harmonize' is used as a substitute for the word 'censorship'. Chinese censorship is often for political reasons, hence the word 'harmonize' is regarded as a milder term, and this is called 'euphemism'.
This word completes the sentence in meaning, hence option C is correct.
Option A: 'Rebuttal' means 'denial', to refuse to accept something.
Option B: 'Patois' refers to dialect, a language that is regional and is used by only the locals from that region.
Option D: A 'hyperbole' is an exaggeration. It refers to words or statements that are blown out of proportion and do not literally mean the same.
These words do not complete the meaning of the sentence. Hence options A, B and D are incorrect.