Read this passage from "The Fall of the House of Usher" by Edgar Allan Poe:

During the whole of a dull, dark, and soundless day in the autumn of the year, when the clouds hung oppressively low in the heavens, I had been passing alone, on horseback, through a singularly dreary tract of country.
Which word contributes to the Gothic tone of the passage?
A. heavens
B. oppressively
C. country
D. singularly