III.
2) was buying
3) was shopping
4) saw
5) threw
6) was working
IV.
3) Holmes was playing her violin when a burglar broke into the house.
4) While Mrs Smith was sweeping the floor she was listening to the radio.
5) Who was reading a book when Holmes shouted 'Help'?
6) Mrs Smith was cleaning the house when the baker knocked at the door.
7) While the dog was chasing the cat, Mrs Smith was sweeping the floor.