Which example best illustrates a prepositional phrase?

A prepositional phrase typically consists of a preposition followed by a noun or noun equivalent, which serves as the object of the preposition. In this case, "To the park" demonstrates this structure perfectly. The word "to" is the preposition that indicates direction, and "the park" serves as the object of the preposition, which completes the idea and provides additional context about where the action is directed.

The other examples do not fit the criteria for a prepositional phrase. "Running fast" functions as a participial phrase, with "running" being a verb that describes an action but lacks a preposition. "The cat sleeps" is a simple sentence about a subject and its action, lacking any prepositional context. Lastly, "She decided to go" is also a complete sentence that includes a verb and a direct action but does not incorporate a prepositional phrase structure. Thus, "To the park" is the clear and correct example of a prepositional phrase.