D. The dying of the fire is making the speaker think of the death of Lenore, and the possible appearance of her ghost.
This line suggests a sense of loss and melancholy, as the "dying ember" can symbolize not only the fading warmth and light of the fire but also the emotional state of the speaker who is reflecting on the death of Lenore. The imagery evokes the idea that the remnants of the fire might be analogous to the lingering memory or presence of Lenore, suggesting the possibility of her ghost or spirit haunting his thoughts.