Answer: A. The tension between Gabriel and the rest of his family.
In this short story, we meet Roy and John. They are forbidden to play on the Rockpile as the other boys do. Nevetheless, Roy decides to go anyway. He gets into a fight and gets hurt, which makes his father, Gabriel, extremely mad. John is not Gabriel's son (he is his stepson) and it is clear that he favors Roy over John. Gabriel blames John and the mother for what happened, and the tension between him and the rest of the family makes the apartment an unsafe place.