Final answer:
Quote C foreshadows the ending of 'To Build a Fire', highlighting the dangers of traveling alone in extreme cold, which is central to the story's conclusion.
Step-by-step explanation:
The quote that foreshadows the ending of "To Build a Fire" is C) "The old-timer had been very serious in laying down the law that no man must travel alone in the Klondike after fifty below." This sentence hints at the potential danger and consequences of the protagonist's situation. In contrast to the other quotes which deal with immediate circumstances, this quote speaks directly to the critical insight about the environment and the risks of travelling alone in extreme cold, which is a central theme leading to the character's downfall.