Answer:In Jack London’s "To Build a Fire," the external conflict of character versus nature is the most important. The man in the story struggles to keep himself alive in the extreme cold of the Yukon. Through the story, London shows how natural forces are indifferent to the survival of humans. He also shows how a human, when unprepared, is no match for nature:
It did not lead him to meditate upon his frailty as a creature of temperature, and upon man's frailty in general, able only to live within certain narrow limits of heat and cold; and from there on it did not lead him to the conjectural field of immortality and man's place in the universe.
Throughout the story, the man’s struggle against the cold drives the plot of the story forward. It affects the man’s ability to think clearly and problem-solve, and it decides his fate. There are instances in the story where the man ignores signs of trouble, such as when he comes across the old sled trail. However, his blind determination to join the others at the camp drives him on:
The furrow of the old sled-trail was plainly visible, but a dozen inches of snow covered the marks of the last runners. In a month no man had come up or down that silent creek. The man held steadily on. He was not much given to thinking, and just then particularly he had nothing to think about save that he would eat lunch at the forks and that at six o'clock he would be in camp with the boys.
This external conflict continues right up to the end of the story, when the man dies from the cold. Thus, the external conflict of character versus nature is most significant to the plot of the story.
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