The correct response is:
It sets up a contrast between Buck’s comfortable life and the harsh conditions in the wild, highlighting the conflict he faces.
Starting Buck's story in California allows the reader to understand his initial comfort and privilege, which sharply contrasts with the brutal reality he faces in the Yukon. This contrast is essential in illustrating Buck's transformation and the struggles he encounters as he adapts to a more primal existence, ultimately reinforcing the themes of survival, instinct, and the call of the wild.