1. A group of students have met their friends at the railway station.
=>Their friends have been met at the railway station(by a group of students)
2. They didn’t allow Tom to take these books home.
=>Tom wasn't allowed to take these books home
3. The teacher won’t correct exercises tomorrow.
=>Exercises won't be corrected by the teacher tomorrow
4. How many trees did they cut down to build that fence?
=>How many trees were cut down to build that fence? 
5. This well-known library attracts many people.
=>Many people are attracted by this well- known library. 
6. All students attended the meeting.
=> The meeting was attended by all students. 
7. People say that he is intelligent.
=>He is said to be intelligent.
8. He can’t repair my bike.
=> My bike can't be repaired by him. 
9. The doctors have operated Tom since 10 o’clock.
=>Tom has been operated by the doctors since 10 o'clock.
10. This is the second time they have written to us about this.
=>This is the second time we have been written to about this.