1/ was walking

2/ attended

3/ was standing

4/ was riding

5/ lived

6/ was walking

7/ was going

8/ was studying ; had

9/ were dancing

10/ were sitting

I'm not sure that all my answer were corrected

But please appreciated it ^^

1. I ____was walking____down the street when it begin to rain

2. At this time last year, I_was attending____an English course 

3. Jim_was standing__under the tree when he heard an explosion 

4. The boy fell and hurt himself while he __was riding_ a bicycle 

5. When we met them last year, they___were living__ in Santiago 

6. The tourist lost his camera while he_was walking_around the city 

7. The lorry ___was going____ very fast when it hit our car 

8. While I__was studying___in my room, my roommate ___was having___ a party in the other room 

9. Mary and I____was dancing__ the house when the telephone rang 

10. We ______were sitting_____ in the café when they saw us