19. My parents bought some beautiful clothes last week.
Some beautiful clothes were bought by  My parents last week.
20. You mustn't use this machine after 5.30 pm.
This machine  mustn't be used after 5.30 pm
21. I will invite some guesses to come to my new house next week.
→ Some guesses will be invited  to come to my new house next week.
22. Some engineers have built this bridge for two years
→ This bridge has been built for two years 
23. People use the Internet all over the world.
The Internet is used  all over the world.