El abuelo a la playa durante los veranos. a. iba b. iban c. ibas

Iba is the conjugation of the verb ir for the third person singular in the imperfect tense. In general, the imperfect is used to talk about past actions, conditions, or events that occurred regularly or frequently or that were in progress in a moment in the past. So grandpa used to go to the beach every summer. Finally:

El abuelo iba a la playa durante los veranos.