"estaba vs. estuvo"
What are the rules?
estaba is imperfect, estuvo is preterit.
The basic rules are that preterit is for what happened at a specific time in the past, whereas imperfect is for something that doesn't have a specific time.
ayer nadamos en el mar. (yesterday, we swam in the ocean)
nadabamos en el rio cada dia (we swam in the river every day)
see preterit vs imperfect :D