Answer: C. Simile.
Step-by-step explanation: a simile is a figure of speech that consists in making a comparison between elements that aren't obviously related, this comparison is made using the words "like" or "as." The given excerpt from "Don Quixote" includes a clear example of a simile, specifically in the phrase "and will keep this precept as carefully as Sunday" it is comparing the care he will put in the precept with the one he puts in Sunday.