The correct answer is A. at midnight while the nightingale sings. He thinks this kind of death would be painless and sweet, enveloped in the ecstatic song of the nightingale. There is a certain amount of grieving at the thought of death, because then he wouldn't have had ears to listen to the nightingale's song. But nevertheless, this moment provides an escape from the grim, disturbing reality - an escape too short, as it turns out at the end of the poem.
