The correct answer is A) How oft, in spirit, have I turned to thee, and, How often has my spirit turned to thee!
Explanation: The speaker refers to a presence in the woods that he turns to when everything about the world seems dark and "joyless", despite the fact that it might be a "vain belief" - that it may not even be real. The theme of this specific stanza is that it doesn't matter if it's real or not, because the "spirit" brought him happiness when he most needed it.