Final answer:
The verb form that completes the second sentence is 'compraban'.
Step-by-step explanation:
The verb form that correctly completes the second sentence is compraban.
When referring to the past and describing actions that happened repeatedly in the past, the imperfect tense is used. In this sentence, 'cuando tenía 12 años' indicates a past action that occurred multiple times. Therefore, the correct verb form is compraban.
Example: Mis padres me compraban juguetes cuando tenía 12 años.
Learn more about Spanish verb forms