I would say the correct answer is A. Passionate Emotion. Keats's poem is essentially about death and the cessation of all earthly beauty. But the more devoted he is to death, the more passionately he craves the beauty that death will take away from him. There is no idealism in this poem, nor is it about goodness and innocence of humanity. There are some elements of nature, but it is not a predominant theme (such as it is in some other Keats's poems).