Chuyển các câu sau sang câu bị động 16. Somebody has bought the presents 17. I have not received a telegram. 18. She has not written a story. 19. She has not cheated anybody. 20. Have you kept the secret? 21. Who has done this? 22. Why have you told a lie? 23. Who has torn my book? 24. Have you written the letter? 25. Has the policeman caught the thief? 26. Has the postal department released a new stamp? 27. Has she phoned him? 28. Have they noticed us? 29. Has the surgeon performed the operation? 30. Have the customers paid you? giúp mình với mình đang cần gấp