câu 11 they were made work very hard by the boss

câu 12 an E work shop have been just held

câu 13  suker the silver medal was awarding by the presiden of fifa

câu 14 this exercise carefully be done 

câu 15 this question can be answered

câu 16

11. The boss made them work very hard.

⇒ They was made to work very hard by the boss.

12. They have just held an English workshop.

⇒ An English workshop has just been held.

13. The President of FIFA is awarding Suker the silver medal.

⇒ Suker is being awarded the silver medal by the President of FIFA.

14. Huong was reading '' Romeo and Juliet '' when we came.

⇒ '' Romeo and Juliet '' was being read by Huong when we came.

15. You must do this exercise carefully.

⇒ This exercise must be done carefully.

16. No one can answer this question.

⇒ This question can't be answered.

17. Mary's parents gave her a birthday present.

⇒ Mary was given a birthday present by her parents.

⇒ A birthday present was given for Mary by her parents.

18. Have they read the letter ?

⇒ Has the letter been read ?

19. Did they have to choose it ?

⇒ Did it have to be chosen ? 

20. Who wrote that play ?

⇒ Who was that play written by ?