Final answer:
The narrator and Stephen travel to the Yukon because they want to make money from the gold rush.
Step-by-step explanation:
The most likely explanation why the narrator and Stephen travel to the Yukon is c) they want to make money from the gold rush. In the late 1890s, there was a gold rush in the Yukon which attracted thousands of people hoping to strike it rich. The allure of quick riches drove many to venture into the harsh conditions of the Klondike region in search of gold.