11. "If you want to learn English, I can help you," John said.

- John said he could help me if I wanted to learn English. 

12. "Where are you studying?" Mr. Bruce asked.

- Mr. Bruce asked me where I was studying.

13. "Please call me at 6 o'clock tomorrow morning," said Mai.

- Mai asked me to call her at 6 o'clock the next morning.

14. "Are you interested in this Language Center?" asked Lan.

- Lan asked me if I was interested in that Language Center. 

15. "We will spend our holiday in Da Lat next month," said Mrs. Chi.

- Mrs. Chi said that we would spend our holiday in Da Lat the next month. 

16. "Do you live here?" Liz asked.

- Liz asked me if I lived there. 

17. "What does your son want to learn?" the man said to Mr. Linh

- The man asked Mr.Linh what his son wanted to learn.

18. "You must come today," Hoa said.

- Hoa told me that I had to come that day.

19. "I don't understand what you are saying," Tom told us.

- Tom told us he didn't understand what we were saying.

20. "There isn't any information about these colleges," Nam said.

- Nam said there wasn't any information about those colleges. 

11. John said if I wanted to learn English, he could help me.

12. Mr. Bruce asked where I had been studying.

13. Mai asked me to call her at 6 o'clock the next/following morning.

14. Lan asked me if I was interested in that Language Center.

15. Mrs. Chi said they would spend their holiday in Da Lat the following month.

16. Liz asked if I lived there.

17. The man asked Mr. Linh what his son wanted to learn.

18. Hoa ordered me to come that day. 

19. Tom told us that he didn't understand what we were saying.

20. Nam said there wasn't any information about those colleges.

Chúc anh/chị học tốt!