Ответ:

1) The postman has already delivered the mail.

The mail has already been delivered by postman.

2) Have the workmen repaired the street lights yet?

Have the street lights been repaired yet by workmen?

3) The government has just passed some new antismoking laws.

Some new anti-smoking laws have just been passed.

4) The local council hasn’t built any new homes fortwenty years.

No new homes have been built for twenty years.

5) Nobody has watered the plants.

The plants have not been watered.

6) Someone stole my bike last night.

My bike was stolen last night.

7) Archaeologists discovered a Roman temple underneath the new housing estate.

A Roman temple was discovered underneath the new housing estate.

8) The sports officials held the races indoors because it was raining.

The races were held indoors because it was raining.

9) Someone had booked the leisure center for a children’s party on Saturday.

The leisure center had been booked for a children's party on Saturday.

10) The plumber was repairing the dishwasher so I couldn’t leave the house.

The dishwasher was being repeired, so I could not leave the house.

11) When we returned to our hotel room, the chambermaid still hadn’t cleaned it.  

Our hotel room still  had not been cleaned when we returned.