Here follows the key to the practice sheet I handed out in class the other day:
42.1.
2. is made 3. was damaged 4. were invited 5. ares hown 6. are held 7. was written... was translated 8. were overtaken 9. is surrounded
42.2.
2. When was television invented?
3. How are mountains formed?
4. When was Pluto discovered?
5. What is silver used for?
42.3.
3.covers 4. is covered 5. are locked 6. was posted... arrived 7. sank... was rescued 8. died... were brought up 9. grew up 10. was stolen 11. disappeared 12. did Sue resign 13. was Bill sacked 14. is owned 15. called...was injured... wasn't needed 16. were these photographs taken... Did you take 17. 'm not bothered / am not bothered
42.4.
2. All flights were cancelled because of fog.
3. This road isn't used much
4. I was accused of stealing money
5. How are languages learned/learnt?
6. We were warned not to go out alone