Answer:
Once forged, loyalty is a powerful opponent for even Buck’s natural instincts.
Step-by-step explanation:
This is the sentence that best presents a strong conclusion. An effective conclusion needs to summarize the information that was presented in the previous paragraphs. Moreover, it should remind the reader of the main idea being discussed to make sure that this leaves a lasting impression on his mind. In this sentence, the author does so effectively, as he reminds the reader of the conflict that Buck experiences between loyalty and his natural instincts.