The subject pronoun you would use when speaking to a friend is "tú."
The subject pronoun "tú" is used when speaking to a friend. To figure this out, you can use your knowledge of Spanish subject pronouns and their meanings. In this case, "tú" means "you" in a casual, informal way and is typically used when speaking to friends or people of a similar age. Other subject pronouns include "usted" (formal "you"), "ello" (it), and "ella" (she).
