Final answer:
Jack London's stories, such as 'To Build a Fire' and 'The Call of the Wild,' primarily explore the theme of the inevitability of death and the struggle for survival against the indifferent natural world, rather than the care for the elderly or the human domination over nature. The correct answer is option: everything that lives must die.
Step-by-step explanation:
One of the themes of Jack London's story is that everything that lives must die. In his narrative works, Jack London often explores the theme of the struggle for survival, echoing the ideas of Darwin about the natural selection process and the harsh reality of the natural world. This theme is especially evident in his famed stories like 'To Build a Fire' and the novel 'The Call of the Wild'. In these stories, characters confront the unforgiving elements of nature, often resulting in the realization of their own mortality and the untamed power of the natural environment.
The notion that the younger generation should take care of the elderly, or that humans will always rule over nature, are not central themes that are consistently present throughout London's works. Instead, his stories tend to emphasize the indifferent and often brutal forces of nature that characters must face, and the instinctive, atavistic qualities that allow them to survive, or that they succumb to in the end.