19/ He will be sent abroad to study
20/ this room was used by her
21/ my bike was stolen yesterday
22/ a letter was received from his parents
23/ this house will be bought by her
24/ my  house aren't built
25/ songs mustn't be sung in the class

Question 19. They will send him abroad to study.
=> He will be sent abroad to study.
Question 20. She used this room.
=>  this room was used b her
Question 21. Someone stole my bike yesterday.
=> my bike was stolen yesterday
Question 22. He received a letter from his parents.
=> a letter from his parents was received
Question 23. She will buy this house.
=> this house will be bought 
Question 24. They aren't building my house.
=> my house isn't being built by them 
Question 25. You mustn't sing songs in the class.
=> songs must not be sung in the class.