Jawaban:

1. Somebody has cleaned the room.

-The room has been cleaned by somebody.

2. They have postponed the concert.

-The concert have been postponed by them.

3. Somebody is using the computer at the moment,

-The computer is being used by somebody at the moment.

4. I didn't realise that somebody was recording our conversation.

-I didn't realise that our conversation was being recorded by somebody.

5. When we got to the stadium we found that they had cancelled the game.

-When we got the stadium, we found that the game had been cancelled by them.

6. They are building a new ring road round the city.

-The city are being built a new ring road round by them.

7. They have built a new hospital near the airport. -A new hospital have been built near the airport by them.

8. We will invite all my friends to my birthday party.

-All my friends will be invited to my birthday by us.