Answer:
A. By having the narrator recall the story's past events and giving hints about what happened
Step-by-step explanation:
The narrator hints that a superior race was envious of us, somehow and wanted something that we had. When he does that, he compares the alien race to humans when comparing humans to mindless beasts. It is clear that the narrator is remembering the beginning of it all and it is more than enough to make the reader tense and wondering what happened.