Which of the following is an example of a metaphor?

The phrase "Time is a thief" serves as a metaphor because it compares the abstract concept of time to a thief, suggesting that time can stealthily take away moments from our lives just as a thief takes valuable possessions. This comparison does not imply that time literally possesses the characteristics of a thief; instead, it conveys a deeper meaning by highlighting how time can be elusive and how it can rob us of our experiences without our awareness.

In contrast, the other options rely on similes or personification rather than metaphors. For instance, "She is as brave as a lion" uses "as" to draw a comparison, making it a simile. "He runs like the wind" also employs "like," indicating a similarity rather than an identity, which characterizes it as a simile as well. Meanwhile, "The sun smiled down on us" attributes human qualities to the sun, which is an example of personification. Thus, only "Time is a thief" properly embodies the qualities of a metaphor by establishing a direct conceptual link without relying on comparative language.