past progressive - function
you use the past progressive for:
situations in the past where a short event happened in an ongoing action. The ongoing action is in the past progressive and the new action is in the simple past.
e.g. While Liz and Sharon were discussing children’s manners, Julie left the office for lunch.
When she came back, the two of them were still talking about the same topic.
actions and events in the past which happened simultaneously over a longer period.
e.g. While the fans were clapping their hands, the popstar was singing his latest song.
Mr Smith was presenting the new concept and everybody was listening.
highlighting the duration of an action in the past.
e.g. I was answering e-mails all morning.