1. When I saw Nick, he was writing a letter.
2. At 2 o'clock my mother Fiona was cooking soup.
3. The father was not sleeping when little Freddie opened the door.
4. At 10 o'clock, Samantha was doing homework.
5. When the old teacher came in, the children were talking.
Нужно подчеркнуть соответствующий вс глагол - was/were (was not/were not) и глагол с окончанием -ing.