B. Vanquish
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.