compared with ,sth,可懂,过去分词短语作状语,相当于sth be compared with,只能用ed的形式
不懂可继续问^~^加一个when 就相当于是一个状语从句，不过这里是状语从句的省略就是，，when it's compared with ,,,,，sth ,,,,,=when compared with ,,,,,，sth ,,,,,,,