Answer: D). The beauty of music sung by Safie for Old Mr. De Lacey.
Throughout the book, we learn that the monster is not all bad. Instead, he is a misguided child-like figure, who has no one in the world who cares for him or loves him in any way. The monster has occasional moments of kindness and sensibility which demonstrate that he is capable of positive feelings. One such example is the pleasure he feels when listening to the music sung by Safie. This shows that the monster is capable of appreciating beauty and art, as well as of having tender feelings.