Answer:
D
Step-by-step explanation:
The literary technique being used in the sentence "The castle wall was a serpent, wrapping around me" is metaphor. A metaphor is a figure of speech that compares two unlike things, suggesting that one thing is another thing, not just like it. In this sentence, the castle wall is being compared to a serpent, suggesting that the wall shares certain qualities with a serpent, such as being long, sinuous, and encircling.