I would say wikihow or youtube don't know for sure so don't depend on my answer :)
Answer:
Option A: "A Horseman in the Sky" emphasizes the killer while "The Death of Reynolds" emphasizes the person killed.
Explanation:
In "A Horseman in the Sky" the story focuses on the soldier who ends up killing a man. It emphasizes the killer, his situation, his fears.
Meanwhile, in "The Death of Reynolds" it emphasizes the person killed, as it's title suggests.
it means that they act on instinct
The answer would be a Participial phrase.