21. Sarah was writing a letter when I came.
->When I came, a letter was being written by Sarah
22. They are building a new ring road round the city.
->A new ring road is being built round the city
23. The manager must sign the cheque.
->The cheque must be singed by the manager
24. John will meet me at the airport.
->I will be met at the airport
25. They have built a new hospital near the airport.
->A new hospital has been built near the airport
26. They think that this book is of no use.
->This book is thought to be of no use It is thought that this book is of no use
27. People believe that he was injured in the accident.
->It is believed that he was injured in the accident
28. They say many people are homeless after the floods.
->It is said that many people are homeless after the floods
29. We believe that he is studying painting in America.
->It is believed that he is studying painting in America
30. People think that he knows English well.
->It is thought that he knows English well.