1) Somebody has stolen my bike.
→ My bike has been stolen.
2) They have postponed the class meeting.
→ The class meeting has been postponed.
3) They have built a new school near our house.
→ A new school has been built near our house.
4) Has somebody informed Lan of the change?
→ Has Lan been informed of the change?
5) They haven't finished their assignments.
→ Their assignments have been not finished.