Here's why:
* Indefinite pronouns refer to nonspecific people or things. Some common examples include *everyone, someone, anyone, no one, nothing, something, anything, all, both, few, many, several, some, most*, and *none*.
* In sentence A, "Neither" is the indefinite pronoun. It refers to two people, but we don't know who specifically.
The other sentences do not contain indefinite pronouns:
* B) Gus liked the music but not Latisha: This sentence uses proper nouns ("Gus" and "Latisha").
* C) Todd and Larissa went to prom: This sentence uses proper nouns ("Todd" and "Larissa").