Réponse :
did you hear
saw
they were playing
what were you doing
was playing
were not playing (ici tu vas pas dire "weren't playing" parce que c'est le discours est formel )
was playing
Explications :
alors c'est simple , quand l'action est longue tu utilise le past continuous ( "to be" in the past simple + gerund ( v+ing)
mais quand c'est une courte action , tu utilise le passé simple
