Answer: True: un día, una tarde ; False: de repente
Step-by-step explanation:
The imperfect can be used to describe events that were happening in the past over time, so we can say:
Un día yo estaba en la playa cuando... (imperfect past)
Una tarde nosotros íbamos al parque y... (imperfect past)
On the other hand, if we want to talk about a specific event that happened in the past, we use the preterit tense.
de repente empezó a llover. (preterite)
de repente vimos a nuestros vecinos. (preterite)
Translation
One day I was at the beach when suddenly it started to rain.
One afternoon we were going to the park and suddenly we saw our neighbors.
Spymore