The traits of a hero are determined by
a. cultural values.
b. their experiences.
c. the plot of the story.
d. their mentors.

The traits of a hero are usually determined by all of these except for C - the plot of the story. 

For that reason, the correct answer is probably a - cultural values, b - their experiences, d - their mentors.

It also makes sense that the different traits every hero has are rather complex when compiled together and the reasons why they have become as they have become have multiple reasons.