1. She did this exercise two days ago.
→ This exercise was done two days ago.

2. They send him abroad to study chemistry.
→ He is sent abroad to study chemistry.

3. Somebody used this room last week.
→ This room was used last week.

4. Someone has stolen my bike.
→ My bike has been stolen.

5. He received a letter from his parents.
→ A letter from his parents was received.

6. She will buy this house next month.
→ This house will be bought next month.