I don't think it is any or much less a sentence.
The answer should be B but i am not for sure.
The story Old Yeller by Fred Gipson is a realistic fiction book. It tells about a fourteen year old boy named Travis who was left in charge of his family and the farm while his papa was away on a cattle drive. One day an old yeller dog shows up and steals some meat and wrecks the fence.
I would have to say it's part of the theme.
Morality and politics is the ethos of the story, aka origin aka theme.
With-out a theme there would be no plot...and no setting.
So...
C. Theme
