Answer:
11. Leroy added the last piece of the puzzle.
12. A cake was baked by my mother yesterday.
13. The gate was guarded by Sir Gawain and his servant.
14. She was not beat by me.
15. This experience will not be forgotten by me.
16. I dont know this one, Sorry.
17. I dont know this one either.
18. The police caught the thief.
19. The birds ate Mr. Harvey's entire stock of seed corn.
20. I dont know this one either