In the choices you have given, the answer could be: C. The prepositional phrase “on the park bench” acts as adjectival phrase.
Preposition defines relationship of the words used in the sentence. Prepositional phrases are words that come alongside the prepositions. A determiner and adjective follows a preposition then by pronoun or noun. This is the object of the preposition. Overall, this makes up a phrase which can be an adjective, adverb, modifying noun, a locator in time or space or a teller of the when or where of events and happenings.