Answer: A. Sinking.
Step-by-step explanation: The tone of a story or a text is the author's or speaker's attitude towards the subject, the audience or even the characters of the text. There are many different kinds of tones, like positive, negative, happy, objective, sad, angry, etc. A gothic tone usually contains elements of fear, horror, death, and gloom, as well as romantic elements, such as nature, individuality, and very high emotion. In the given passage from "The Fall of the House of Usher" by Edgar Allan Poe, the word "sinking" contributes to the gothic tone.