Answer:
1. había estudiado
2. habíamos comido
3. te habías mudado
4. habían visto
Step-by-step explanation:
Pretérito pluscuamperfecto tense is used in Spanish to express the priority of a past action over a past one.
Being a compound tense, it is formed with the auxiliary "haber" and the participle of the main verb. On this occasion, the verb "haber" appears in the past tense.