Final answer:
The correct pronoun to complete the conversation is 'los'
Step-by-step explanation:
The correct pronoun to complete the conversation is O. los.
In the conversation, Juan is asking if Eric knows the history teacher, so the pronoun that Eric should use to refer to the teacher is masculine plural.
In Spanish, when referring to a group of males or a mixed group of males and females, the pronoun 'los' is used. Therefore, Eric should respond with 'Sí, yo los conozco'.
Learn more about Spanish pronouns