Formation of the past continuous
Positive sentences
Subject + was/were + verb(ing)
They were talking about her when she walked into the room.
Negative sentences
Subject + was/were + not + verb(ing)
Subject + wasn't/weren't + verb(ing)
He asked me why I was not having dinner at the hotel.
We weren't playing football when the earthquake began.
Was/were + subject + verb(ing)
Was she going to the theatre when it started raining?
Exceptions in spelling
Final 'e' is dropped (but: 'ee' is not changed)                               
Рис. \(1\). Come                                     
come – coming   
(but: agree – agreeing)                         
After a short, stressed vowel, the final consonant is doubled
Рис. \(2\). Sitting
sit – sitting
'L' as a final consonant after a vowel is doubled (in British English)
Рис. \(3\). Travelling
travel – travelling
Final 'ie' becomes 'y'
Рис. \(4\). Baby lying
lie – lying
Signal words: 'when', 'while', 'as long as'.
Рис. 2. Sitting, https://pixabay.com/images/id-2763547/ Pixabay License CC0
Рис. 3. Travelling, https://pixabay.com/images/id-4399206/ Pixabay License CC0
Рис. 4. Baby lying, https://pixabay.com/images/id-33252/ Pixabay License CC0