1. I was reading a book when I heard a strange noise.
2. While we were swimming it started to rain.
3. I was getting ready for the party when my friend phoned me.
4. We were shopping when we saw them.
5. ?
6. I found this key while I was tidying up my room.
7. My father and I were playing chess when my cousins arrived.
8. My mom was having tea with her friend when I arrived.