John has finished his homework .John's homework has been finished by him.we must do something to protect the environment.Something must be done to protect the environment.被动语态 要怎么去理解啊先说 主动语态，就是谁 做了什么那么相对的，被动语态，就是 什么被谁做了那有什么格式的么？动词的形式分三种现在时，过去时，过去分词被动语态中，要用动词的过去分词的形式