I looked for the phone when I was hearing a knock on the door.
I was lookING for the phone when I HEARD a knock on the door.
My mum were cooking when I came back home.
My mum WAS cooking when I came back home.
I could to rollerblade five years ago.
I COULD ROLLERBLADE five years ago.
I can type when I was 8.
I COULD type when I was 8.