Final answer:
The quote mentioning 'graveyard flowers' and their scent speaking 'the names of our dead' uses nature to create a dark tone.
Step-by-step explanation:
The quote that best reflects how the author uses nature to enhance the dark tone of the story is: "The last graveyard flowers were blooming, and their smell drifted across the cotton field and through every room of our house, speaking softly the names of our dead."
This excerpt uses imagery associated with death (graveyard flowers) and the sensory detail of their smell penetrating living spaces to evoke a somber and dark mood. The mention of the dead makes this option particularly potent in establishing a dark tone in relation to nature.