Final answer:
The appropriate imperfect form of the verb 'Ir' is 'iban'.
Step-by-step explanation:
El imperfecto is used to talk about past actions that were ongoing, repeated, or habitual. In this case, the sentence is describing a regular action that happened in the past, so we need to use the imperfect form of the verb ‘ir’. The correct answer is option C, ‘iban’.
Learn more about Spanish verb conjugation