I believe it would be B, vanquish. For one to use such a fancy and strong word, would sound as if one were boasting. Example: "The young man brazenly claimed that he had vanquished the massive bear."
The word “boastful” means to speak with exaggeration. Another way to consider boastful is writing with “purple prose” or “flowery” language, which is the use of language that draws attention to itself. Of all four of the potential responses, “vanquish” is a term that could, in fact, be considered a bit too elaborate and call excessive attention to itself “beat,” “defeat,” or “overcome” could have sufficed.
