D) personification
Personification is giving a non-human thing human-like traits. The city is not a human, but sleeping is. Therefore the description of the city uses personification. Another example of personification is: "The cloud cries down on the valley."
An allusion is a reference to another published work. If a relationship is described as "star-crossed", it would be an allusion to Romeo and Juliet.
A flashback is an interruption in a story to tell about something that has already happened. Often flashbacks are used to give background information about a character to better understand his/her motivation.
An allegory is a story with a double meaning.