Prepositional phrase as adjective or adverb phrase?

Please if any one could help
Thank you in advance

Circle the adverb or adjective phrase in each sentence, then tell what kind it is.

My question is : Which is the preposition phrase in the question below doing the function of adverb or adjective phrase ?
Many of the viewers responded to the poll.
I suggested (( to the poll )) = ADV phrase modifying the verb responded, but as you see one book mentioned it can be the focus on ( Many ) = pronoun and here ( of the viewers ) can tell who are those viewers ? = those who are responded to the poll and not other ones. So, perhaps it is understood on this way or on the way I mentioned first.