O Past Continuous é usado para expressar um evento ou ação em progresso em um momento específico no passado.
I was reading my favorite book last night.
It was raining a lot when we left.
What were you doing at 10 a.m.?
Yesterday, at 5 o' clock, I was going to the mall.
Para expressar a interrupção de uma ação ou evento de longa duração, podemos combinar o Simple Past e o Past Continuous:
She was leaving when I arrived.
He was going to bed when the phone rang.
I cut myself when I was shaving.
Mas se a idéia a ser transmitida é de que mais de um evento estava ocorrendo simultaneamente, devemos utilizar o Past Continuous em todas as sentenças.
I was not listening when he was talking to you.
He was working while his wife was shopping.
While John was washing the car, David was painting the porch and Elaine was planting some flowers.
Podemos também usar o Past Continuous para descrever uma situação ou ambiente no passado, transmitindo a idéia de simultaneidade novamente:
When I was at the park, birds were flying, kids were playing, ladies were chattering and couples were holding hands.
Podemos ainda usar o Past Continuous para expressar uma idéia ou opinião, normalmente com má conotação, transmitindo a idéia de rotina, repetição.
The neighbour's dog was always barking.
She was always complaining about the weather.
It was always raining during my trip to England.
Para formar sentenças no Past Continuous, usamos as seguintes regras:
Afirmativa: was verbing , were verbing => to be (Simple Past) + verbo principal no gerúndio.
We were working hard during the campaign.
She was dancing when you played that song.
Negativa: Adicione "not" depois do verbo auxiliar. was not verbing , were not verbing
He was not listening to what you were saying.
We were not fighting when she came.
Interrogativa: Inverta o verbo auxiliar e o sujeito.
Were you sleeping when I rang the bell?
Was she working during the exibition last night?
Note que existem algumas expressões indicadoras deste tempo verbal, sendo as mais comuns: when, while, during.
Exercises on the above theory
Exercícios sobre a teoria acima