The correct answer is B. Once upon a midnight dreary, while I pondered weak and weary,
Over many a quaint and curious volume of forgotten lore—
Step-by-step explanation:
In poetry and other types of literary works, the tone is mainly established through the description of the setting, the use of words and others that define the attitude of the author towards the elements described in the text and is also linked to the general atmosphere.
In the case of the poem "The Raven" by Edgar Alan Poe the tone in this is mainly dark and gloomy and this is mainly created in the section "Once upon a midnight dreary, while I pondered weak and weary, Over many a quaint and curious volume of forgotten lore—" because in this the setting is described "midnight dreary" which is linked to darkness and also the detail "while I pondered weak and weary" supports the general gloomy and dark tone of poem; besides this, these lines are the first ones in the poem and therefore the first element that describes and sets the tone that is preserved during all the poem.