I believe the correct answer would be the last option. The rhetorical device that is seen in the given statement above would be antithesis. It is a literary device that involves the use of two that are opposite of each other in a statement in order to attain a contrasting effect. It is used in texts as it strengthens the argument. Also, it creates emphasis and a sense of balance of the words in the text. The words used here are light and darkness. Other examples are a quote of Aristotle which says that "Patience is bitter but it has a sweet fruit" and a quote by Neil Armstrong which says "That's one small step for man, one giant leap for mankind."
