Special note,
blow is a change of state verb:
The storm has blown the tree down. (Active)
The tree has been blown down by. (Passive)
The tree has blown down. (No Agent)
Change-of-State
Active: The storm has blown
the tree down.
Passive: It has been blown down <by the storm>.
Ergative:
It has blown down. <no agent>
1. It is stormy. The roof
has blown off! <ergative>
2.
The tree was lying across the road.
It has been blown down in the storm, by the strong winds. <passive, and the subjects are the same

, which is why passive voice is used.>