一、做定语,或定语从句
The kidnappers were using a stolen car. (steal过去分词,做定语)
The name mentioned in the letter was unknown to me.（mention过去分词,定语从句）
二、固定用法
hand-written letters手写信件
underdeveloped regions欠发达地区
三、做表语
As we joined the big crowd I got （separated） from my friends.