11. They smile at the girl as she walks by

Ko biết làm vì tài liệu ghi là smile, cry, ... => những từ này thì câu không có dạng bị động.

12. They don't keep the bicycle in the garage.

The bicycle isn't kept in the garage.

13. People speak well of your friend.

Your friend is spoken well of

14. Teens think that money is the most important thing in life.

It is was thought that money is the most important thing in life.

15. They make robots from strong metal.

Robots are made from strong metal.

16. Factories use robots because they are reliable.

Robots are used by factories because they are reliable

17. Robots will never attack human beings.

......

18. They had to close that factory because the firm went bankrupt.

That factory had to be closed because the firm went bankrupt

19. Someone made this dress in Spain.

This dress was made in Spain

20. They must blow up part of the tunnel.

Part of the tunnel must be blown up

21. They are solving the problem now.

The problem are being solved now

22. They allowed the students to leave earlier on Thursday.

The students were allowed to leave earlier on Thursday.

23. The police have questioned the suspect.

The suspect has been questioned by the police

24. Lots of people  use mobile phones.

Mobile phones are used 

25. They cut the grass this morning.

The grass was cut this morning