Final answer:
The indefinite pronoun in the given sentence is 'little,' which refers to not much of what is being said being worthy of attention.
Step-by-step explanation:
An indefinite pronoun is a pronoun which does not have a specific, familiar referent. Indefinite pronouns are in contrast to definite pronouns. Indefinite pronouns can represent either count nouns or noncount nouns. They often have related forms across these categories: universal, assertive existential, elective existential, and negative.
The indefinite pronoun used in the sentence "People are saying all sorts of things, but little is worth listening to." is little. Indefinite pronouns refer to persons, places, or things in a more general way than specific pronouns. They don't point to any noun in particular.
In this case, little functions as an indefinite pronoun conveying the idea that not much of what is being said is valuable or worthy of attention. On the other hand, people and all are not functioning as indefinite pronouns in this sentence. People is a plural noun and all is a determiner modifying sorts. Therefore, the correct answer is (C) Little.