Answer:
Add a subject and verb
Explanation:
The group of words does not express a complete thought but can be corrected by adding a subject and a predicate. For instance, the following revision includes the subject Michelle and the verb ran:
Michelle ran with her friends across the wooden bridge.
The rest of the choices are incorrect because adding an adjective, an adverb, a prepositional phrase or a transitional phrase still does not help form a simple sentence that conveys a complete thought.