I,
1. saw
2. were you doing
3. didn't visit
4. rained
5. was reading
6. ate pizza
7. were running
8. Did you find
9. was she dancing
10. were watching
II,
1. called/wasn't/was studying
2. didn't hear/ was sleeping
3. was shining/were singing
4. were talking/walked
5. weren't/were playing
6. fell/was reading
7. was snowing/ shined
8. was shovelling/brought

9. had/was driving/ hit
10. decided/starved
11. were waiting/ arrived
12. was swimming/saw
13. Were,,playing/ started
14. were driving/stopped
15. was blowing//went
III,
1. were building
2. was driving
3. was chatting/was teaching
4. was watching
5. was preparing
6. were ..doing
7. were .. doing
8. didn't go
9. wasn't doing
10. was reading/was playing
IV,
S + was/were + Ving 
1. They were playing tennis at 10.30 yesterday morning
2. Ann was doing homework at 5 o'clock this afternoon
3. My father was washing car from five to six
4. This time last year we were living in France
5. I was cooking dinner half an hour ago
6. The students were offering flowers to the visitors
7. She was working in the studio at that time
8. What were you doing from 3 to 6 yesterday afternoon?

Bài I:

=>

1saw
2were you doing
3didn't visit
4rained
5was reading
6ate pizza
7were running
8Did you find
9was she dancing
10were watching