The odd one out is C, REB. The other options are all acronyms for common English words or phrases. AOT stands for "at the outset," CPA stands for "certified public accountant," TIW stands for "to each his own," and QUD stands for "question under discussion." REB, on the other hand, is not an acronym for any common English word or phrase. It is possible that it is an acronym for a technical term in a particular field, but without more information, it is impossible to say for sure.