Final answer:
The correct verb form that completes the conversation is 'compraste'.
Step-by-step explanation:
The correct verb form that completes the conversation is compraste.
In the conversation, Matilde asks if Olga went to the mall yesterday, and Olga responds with 'Si.' which means 'Yes.' Olga then follows up with 'compraste unas camisetas' which means 'You bought some shirts.'
In this case, 'compraste' is the correct verb form because it agrees with the second-person singular subject 'tú' (you) in the past tense.
Learn more about Spanish verb forms