C. pun
A pun is a literary device where the author takes advantage of two words that sound the same yet have different meanings. This is done in effort to insert comedy into writing. An example of a pun is “I told a story about static electricity, and it was shocking.” The pun here is “shocking” because of how it means appalling as well as a jolt of electricity. With that in mind we can see the title of the play has a pun—“Earnest.” The pun exists because Earnest is both a name within the play as well as sincere.