Final answer:
The most appropriate object pronoun to fill in the blank in the dialogue is 'lo'.
Step-by-step explanation:
The most appropriate object pronoun to fill in the blank in the dialogue is lo. The sentence would then be: "Sí, lo tengo." Object pronouns are used to replace direct objects in a sentence, and in this case, the direct object is "tu boleto." The pronoun "lo" is used to refer to a masculine singular direct object.
Learn more about object pronouns in Spanish