Final answer:
The correct preterite form of the verb is 'fueron'.
Step-by-step explanation:
The most appropriate preterite form of the verb for the given sentence is OA. fueron.
The subject of the sentence is Andrés y Carlos, which is a third person plural. In Spanish, the preterite form of the verb 'ir' (to go) for third person plural is 'fueron'.
Example: Andrés y Carlos fueron a la biblioteca el viernes para estudiar. (Andrés and Carlos went to the library on Friday to study.)
Learn more about Spanish verb conjugation