The correct answer is The source of the noise is not yet revealed, as no one is standing at the door.
We know that the narrator heard someone knocking on his door, however, when he came to open it, there was no one there. So we feel suspenseful as we want to know who was it there in front of his door. We will find out soon enough that there was actually a raven knocking on his window.
Answer:
Noun is a naming word
Adverb is a word which describes the verb
Adjectives is the word that show the quality of noun and pronoun