过去分词作表语时,相当于形容词,表示状态,但是被动语态里的过去分词是动词的一种变化形式,表示被动的动作.如：
The composition is well written.
These articles are all sold out.
The problem is solved.
过去分词作表语,前面的be动词常用现在一般时和过去一般时,被动语态可以用于其它时态：
I have been driven to it.
过去分词作表语,可以被very所修饰：
He was very agitated.
过去分词作表语有主动意义,可以是反身动词,或与介系词搭配.
She is resolved to become a ballet dancer.
The open square was bathed in light.
He was puzzled about it.
I didn't enter the school because it is located in the suburbs.
The door was closed.
The road was mended.
希望我能帮助你解疑释惑.