Final answer:
The old-timer on Sulphur Creek advised the protagonist in 'To Build a Fire' to never travel alone in the Klondike when it is fifty degrees below zero. The correct option is 3.
Step-by-step explanation:
In Jack London's "To Build a Fire," the advice given by the old-timer on Sulphur Creek to the protagonist was to never travel alone in the Klondike when the temperature dropped below fifty degrees below zero.
Despite initially dismissing the old-timer's warning as overly cautious, the man in the story comes to realize the truth and value of the advice as he struggles to survive in the harsh conditions after an accident leaves him in peril.
This advice is a crucial detail of the story, emphasizing the theme of the relentless natural world and the importance of heeding experienced wisdom when facing its challenges.