Read the sentence.

The function of prepositions is to indicate the relationship among pronouns and nouns. In contrast, a prepositional phrase begins with a preposition and concludes with the object of the preposition, including one or more descriptors.

Thus, the precise breakdown of the sentence, "In a feeding frenzy, the pigeons descended upon the breadcrumbs that the kindly old man on the park bench continued to toss." is The prepositional phrase 'on the park bench' serves as an adjectival phrase.

The prepositional phrase functions either as an adjective or adverb when it responds to the question, "which one?"

Therefore, addressing the question "which bench?" results in "on the park bench".

The appropriate response for the question presented above is: "The prepositional phrase 'to toss' functions as an adverbial phrase." <span>In a feeding frenzy, the pigeons came down on the breadcrumbs that the generous elderly man on the park bench kept tossing.</span>