Final answer:
To determine the correct possessive adjective for 'es' (yo), use 'mi' to indicate possession.
Step-by-step explanation:
To determine which possessive adjective to use with the pronoun 'es' (yo), we need to identify the correct possessive adjective for the first person singular. The correct possessive adjective is 'mi'. Therefore, the correct sentence is 'Es mi libro.' The pronoun 'yo' is replaced with 'mi' to indicate possession.
Learn more about Possessive Adjectives