Chuyển câu chủ động thành bị động

1) I'm sorry, I can't answer the difficult question
2) Why Didn't You clean the floor before having lunch.
3) The assistant didn't translate the letter into Vietnamese
4) The staffs have to attend the meeting on Sunday
5) How many students did you teach. Bill?
6) What happened when you closed the window?
7) They have not met her since you appeared
8) Have you told thêm the truth about accident?
9) Is she listening to folk song?
10) will you lend him some money
11) people say that she is the most intelligent girl