Identifying an Oxymoron

In the study of literary devices, both paradox and oxymoron are used to create meaning through seemingly contradictory terms or ideas. A paradox is a statement that appears self-contradictory but may reveal a deeper truth. An oxymoron, on the other hand, is a figure of speech in which two opposite ideas are combined to create an expressive phrase.

Which of the following phrases is an example of an oxymoron?