Answer: B) oxymoron.
Step-by-step explanation: An oxymoron is a figure of speech in which apparently contradictory terms appear in conjunction (together in a phrase or sentence). In line 5 of "Sea Lullaby" by Elinor Wylie, we can see the phrase "A treacherous smiler" this is an example of an oxymoron because someone treacherous is guilty of or involving betrayal or deception, which seems contradictory with someone that is a "smiler."