Final answer:
The correct imperfect conjugation of the verb 'leer' in the sentence is 'leían'.
Step-by-step explanation:
The correct imperfect conjugation of the verb leer in the sentence 'Los abuelos leían el periódico' is leían. In Spanish, the imperfect tense is used to describe ongoing or repeated actions in the past. The verb leer means 'to read' and when conjugated in the imperfect tense for third-person plural, it becomes leían.
Learn more about Spanish verb conjugation