In "The feather pillow" by Horacio Quiroga when the parasites don't have a human to feed on they usually are small, they are parasites of feathered creatures. This parasite, in particular, has been feeding on Alicia's blood, that is why it became so monstrous. We learn about this in the last parragraph of the story.
You are right. the answer is D
The 'rising action' of a novel is the section of the story after the exposition that builds the story's primary (and secondary) conflicts, advancing the plot. This contrasts with 'falling action', the events that come after a story's climax, leading towards a resolution.
