Final answer:
The main conflict in 'To Build a Fire' is Character vs. Nature, representing an external conflict between the protagonist and the extreme elements of the Yukon wilderness. The story's climax occurs when the man fails to build a fire, indicating his impending defeat by nature. The correct answer is option 4) Character vs. nature.
Step-by-step explanation:
The primary conflict in the story 'To Build a Fire' is Character vs. Nature. This is an external conflict where the protagonist faces the brutal and unforgiving force of nature in the Yukon wilderness. The man's struggle to survive against the harsh conditions of extreme cold and snow represents the central tension of the story.
There is a clear battle for survival against the elements, which underscores the man's insignificance in the face of the natural world and highlights the theme of human vulnerability.
The story reaches its climax as the man realizes he has lost his battle with the cold after failing to build a sustaining fire due to the natural elements around him. This moment of the story is the point of greatest tension and marks a major turn of events as it becomes clear that the man may not survive his ordeal.