Answer:
B. Foreshadow the death of the signalman at the hands of the narrator.
Step-by-step explanation:
The specific phrase "This put the monstrous thought into flight" indicates that the narrator is planning something horrible. He knows that the signalman is scared of him. The monstrous thought is most likely murder.
If this doesn't help, I apologize! Context clues will always help with the situation that you're studying.