I have a question regarding to passive voice.
The door opened.
A valley enclosed by tall mountains.
These are passive sentences, aren't they? But why did we not say "The door (verb to be) opened" and the same thing with the second example.
Why is it deleted? What is the difference if we say: The door is opened & A valley is enclosed by tall mountains. Do they have the same meaning with previous examples?
What do we call this kind of cases? & When do we use it?
Thank you in advance,