P vs. I (Palabras Claves)

Select if the key word would be used with the preterite or the imperfect: la semana pasada

Select if the key word would be used with the preterite or the imperfect:
de vez en cuando

Select if the key word would be used with the preterite or the imperfect: hace 3 años

Select if the key word would be used with the preterite or the imperfect: por 15 minutos

Select if the key word would be used with the preterite or the imperfect: todos los viernes

Select if the key word would be used with the preterite or the imperfect: el 30 de abril

Select if the key word would be used with the preterite or the imperfect: rara vez

Select if the key word would be used with the preterite or the imperfect: frecuentemente

What does por fin mean and does it signal the preterite or the imperfect?

What does the key word mientras mean and does it signal the preterite or the imperfect?