1. In the past they had to make bridges out of stone to last for a long time.
In the past bridges had to be made out of stone to last for a long time.
2. The Romans built stone bridges two thousand years ago.
Stone bridges were built by the Romans two thousand years ago.
3. People have used this wooden bridge for ages.
This wooden bridge has been used by people for ages.
4. They use explosives for tunnels in very hard rock.
Explosives are used for tunnels in very hard rock.
5. You must not remove this extinguisher.
This extinguisher mustn't be removed.
6. The workers will finish the tunnel on time.
This tunnel will be finished on time.
7. You can employ a simple cut-and-cover method for shallow tunnels.
A simple cut-and-cover method can be employed for shallow tunnels.
8. A famous architect has designed the tower.
The tower has been designed by a famous architect.
