Here are the completed sentences using the past continuous form of the verbs provided:

1. The tourists **were visiting** the Buckingham Palace when it started to rain.
2. The security guard **was observing** the car park using CCTV at that time.
3. There was a big fire while the workers **were studying** the cathedral.
4. I beg your pardon – what did you say? I **wasn't listening**.
5. When you entered the room, we **were discussing** the importance of keeping traditions alive.
6. Peter **was driving** on the bus when we arrived at the Colosseum.
7. While my friends **were watching** a documentary about ancient castles, I was playing video games.
8. The children **were studying** for their history test when the lights went out.
9. The host **was cooking** some traditional Italian dishes while the guests were chatting.
10. **Were** you **sleeping** home at 7 o'clock yesterday evening?