The figurative language used is a metaphor. A flashback refers to a previous event and there's no indication of Orwell referring to any previous events in this sentence. An oxymoron is when contradictory words are used in a conjunction such as faith unfaithful kept him falsely true. The word usage in this sentence isn't contradictory as it flows well in this sentence. A euphemism is a nice way to say a bothering statement. The sentence isn't any sort of bad claim, so the option of a euphemism is out of the question. A metaphor compares two things without using the words "like" or "as". In this sentence, Orwell compares advertising to the rattling of a stick inside of a swill-bucket. This makes metaphor the correct answer. Hope this helped :))