The question asks us to identify which option is an example of a metaphor. A metaphor is a figure of speech that directly compares one thing to another for rhetorical effect, stating that one thing is another, even though it is not literally true. This comparison often helps create a vivid image or idea in the listener’s or reader’s mind.
Therefore, the correct answer is "Time is a thief" as it accurately employs a metaphor to give a figurative meaning to time by comparing it to a thief.