Answer:
The wistful nature of the man's final thoughts illustrate the human cost of the gold rush.
Step-by-step explanation:
An objective statement is the one not influenced by personal feelings or opinions.
The first detail is not objective as it contains a personal opinion about descriptive writing (... is an excellent example of...).
The second detail tells about the narrator's personal feelings (I was heartbroken...).
The third detail contains another personal opinion, this time about London's narrative abilities (London is masterful...).
The only detail that is stated like a certain fact that no one could have a different opinion or feelings about is the last one: The wistful nature of the man's final thoughts illustrate the human cost of the gold rush.