| 1 | The roof of the tunnel caved in (on the workmen). | |
| 2 | Well, do you remember how the school collapsed? | |
| 3 | Or is it only an accident that most bridges do not collapse? | |
| 4 | Why is he intent upon constructing bridges that do not collapse? | |
| 5 | The ceiling collapsed and rubble poured into the room. |