Answer:
The correct option is prepositional phrase
Step-by-step explanation:
A prepositional phrase is commonly defined as a series of words constituted by a preposition and a noun or pronoun which represents its object.
Bearing the above in mind it could be said that in the sentence "All three newspapers require paid, online subscriptions for people to read content", "for people" correspond to a prepositional phrase, since for is a preposition and people is a noun that represents its object.